|QB 46 
M44 



SLEMENTARY ASTRONOMY : 



MPANIED BY 



SIXTEEN COLORED MAPS, 



EACH 3 BY 3# FEET, 



rHATE THE 



iCHANISM OF THE HEAVENS, 



■ 



i 1 BIIC LEC 1 I'RERS, PRIVATE LEARNERS, ACADEMES 
A'D SCHOOL . 



BY H. MATTISON. 



NEW-YORK : 
HT NTINGTON AND SAVAGE. 

1847. 



# LIBRARY OF CONGRESS. 



• 



"{|lta F ...QB4b 1 nc ! wJa 

♦ 

i UNITED STATES OP AMERICA. 



333. 

ELEMENTARY ASTRONOMY; 



ACCOMPANIED BY 



SIXTEEN COLORED MAPS, 

EACH 3 BY 3% FEET, 

DESIGNED TO ILLUSTRATE THE 

MECHANISM OF THE HEAVENS, 

AND FOR THE USE OF 



PUBLIC LECTURERS, PRIVATE LEARNERS, ACADEMIES, 
AND SCHOOLS. 



BY H. MATTISON. 



NEW-YORK : 

HUNTINGTON AND SAVAGE, 



*£>&£+*&& **i l 2k 







Entered, according to Act of Congress, in the year 1846, 

By H. MATTISON, 

In the Clerk's Office of the District Court for the Southern District 
of New- York. 



£> © 4r 



Leavitt, Trow & Co., Printer*- 
33 Ann-atreet, N. Y. 

if — 






PUBLISHERS' NOTICE. 



As this book may fall into the hands of asome who have not seen 
the Maps by which its lessons are illustrated, it is proper to say that 
the size of the maps is such as to admit of their being studied to 
good advantage at the distance of from twenty to forty feet. Hence 
one set of maps is sufficient for a hundred scholars, and they may 
all study them at the same time, without touching the maps, or say- 
ing a word to each other. The book will furnish all the necessary 
explanations. 

Their number is such as to warrant the belief that the subject 
may be well illustrated by them. They contain, respectively, from 
ten to fifty distinct figures each ; and being executed in white relief 
upon a black groundwork, they not only answer to the appearance of 
the heavens in the night, but admit of being tinted so as to corres- 
pond with every hue observable in the heavenly bodies, and with 
every sentiment or principle to be illustrated. 

The style and execution of the maps is worthy of the subject. 
Though mostly original, and designed by the author from actual 
telescopic observations, they are drawn and engraved by the best 
artists in the country. They are not mere outline sketches, rough 
and unfinished in their appearance, but large and well executed en- 
gravings, beautifully colored. No pains cr cost have been spared to 
make them rich and handsome, as well as adapted to use. Aside 
therefore from their scientific merits, they are decidedly beautiful ; 
and would be a cheap and tasteful ornament for the private mansion, 
as well as for Public Halls, Libraries, Lyceums, &c. 

Every set of the maps will be accompanied by a neat case, in 
which they will be put up, with a cover hung upon hinges ; and a 
hook, or lock and key, to secure them from dust and exposure while 
not in use, and from injury in transportation. Each map will have 
its number where it can be seen when it is rolled up ; to obviate the 
necessity for unrolling them to find any particular one that may be 
wanted. 



IV PUBLISHERS NOTICE. 

They will be put up in two different styles, to accommodate pur- 
chasers. The best will be put up with cloth backs, and mounted on 
rollers ; the price of these, including the case and one copy of the 
book, will be $20 00. 

The second style will be printed on strong paper, colored the 
same as the first, with light slats or rollers at the top and bottom ; 
and the edges bound with tape or ribbon. This quality will be sold at 
$15 00, and will be equal to the first, excepting the cloth backs. 

During the early part of the enterprise the Publishers entertained 
the hope that the work might be afforded at prices even lower than 
these ; but, such has been the expense of its publication, beyond 
what was anticipated, that it is found impossible to retail it lower 
than as above stated, and make the usual discounts to agents and 
other dealers. 

Wherever the maps are purchased and it is found difficult to 
obtain a supply of books in the vicinity, either request some Book- 
seller or Merchant to procure a supply for the district, or send an 
order, containing the cash, direct to the Publishers, 216 Pearl-street, 
New-York. The order should specify how the package is to be 
sent — by Express or otherwise — and to whom it should be directed ; 
and whenever Trustees or Teachers are obliged to take this course 
to supply their schools, the books will be sold to them, even in small 
quantities, at the wholesale price. 

New- York, February, 1847. 



PREFACE. 



The object of the following pages, and the accompanying 
maps, is the introduction of the sublime study of Astron- 
omy into the Domestic Circle, the Lyceum, the Lecture 
Room, and the Primary Schools of the country. That this 
laudable work has already been attempted by others, and 
with a measure of success, is freely admitted ; but at the 
same time it cannot be denied that, comparatively speaking, 
very little has been effected. While it is almost univer- 
sally acknowledged, on the one hand, that no department 
of science is so well calculated to arouse and expand the 
intellect, enlarge the field of thought, awaken a thirst for 
knowledge, and improve the heart ; it may be affirmed 
without hesitancy, on the other hand, that no important 
branch of study is so generally neglected in primary educa- 
tion, as is that of Astronomy. For this there must be some- 
where a sufficient reason — an adequate cause. 

Of the practical advantages of this noble science, there 
can be no rational doubt. It is of immense utility in 
Geography, in Navigation, in Agriculture, in Chronology, 
in the propagation of Religion, and in the dissipation of 
Superstitious Notions. It unfolds to us the most striking 
displays of the perfections of Deity ; it exhibits the gran- 
deur and extent of God's universal empire ; its disclosures 
afford subjects of the most sublime contemplation, and thus 
tend to elevate the soul above vicious passions and grovel- 
ling pursuits; it tends to moderate the pride of man, and 
thus to prepare the soul for the employment of a future 
state. Such, then, is the obvious practical importance of 



vi Preface, 

this study, that it must sooner or later be regarded as an 
essential branch of popular education ; and we apprehend 
the time has already come when an attempt to introduce 
it generally into the Primary Schools of the land, will re- 
ceive the hearty co-operation of every friend of Youth. 

The method, adopted by the author is the one in general 
use in other departments of science. Black-boards, dia- 
grams, outline maps, and visible illustrations, are now con- 
sidered indispensible in the school-room. i; Whenever in- 
struction can be conveyed through the eye," says Pro- 
fessor Smith, " that one of the external senses through 
which the impressions conveyed to the mind are the most 
vivid and permanent, it must surely be best to employ it." 
:t The eye" says another distinguished teacher, "is the 
only medium of permanent impression." These doctrines 
are constantly verified by experiment. In his successful ca- 
reer in this country, as a scientific lecturer, Dr. Lardner con- 
stantly depended upon diagrams to illustrate his public dis- 
courses. Especially were they found necessary in the 
department of Astronomy, his favorite study. 

As a further testimonial in regard to the value of maps 
and diagrams, take the following from Professor Olmsted's 
Treatise on Astronomy : 

"Diagrams for public Recitations. — As many of 
the figures of this work are too complicated to be drawn on a 
black-board at each recitation, we have found it very conve- 
nient to provide a set of permanent cards of paste-board, on 
which the diagrams are inscribed on so large a scale, as to be 
distinctly visible in all parts of the lecture room. The 
letters may be made with a pen, or better, procured of the 
printer, and pasted on. The cards are made by the book- 
binder, and consist of a thick paper board about 18 by 14 
inches, on each side of which a white sheet is pasted, with 
a neat finish around the edges. A loop attacked to the 
top is convenient for hanging the card on a nail. Cards 
of this description, containing diagrams for the whole 
course of mathematical and philosophical recitations, [in- 
cluding Astronomy of course] have been provided in Yale 



PREFACE. Vii 

College, and are found a valuable part of our apparatus of 
instruction." 

These cards, it will be seen, are only one sixth as large 
as the maps accompanying this work, and yet they are 
considered a valuable part of the apparatus of Yale Col- 
lege. But their value is estimated by their utility, and 
not by their cost. 

In regard to the claims of the Elementary Astronomy 
and the accompanying maps, it is the opinion of the author, 
of course, that they possess decided advantages over all 
other works upon this subject now before the public. Nor 
is this said to disparage or make war upon them. By no 
means. Many of them are doing good service, and we 
rejoice in their labors. But as we have adopted a new 
method, it is neither censorious nor immodest to consider it 
one of superior utility. 

But it may be due to the reader to state frankly what 
those distinguishing features are, relying upon which, we 
venture to put forth another elementary work upon this 
subject : 

1. As already intimated we have the most abundant 
and striking illustrations, presented in an attractive form, 
and upon a scale sufficiently ample to be visible in every 
part of the largest school-room, by day or by night. Six- 
teen maps each three by three and a half feet, and contain- 
ing respectively from ten to fifty distinct figures, all devoted 
to the illustration of one general subject, afford scope suffi- 
cient to do it good justice. Besides, many of these draw- 
ings are entirely original, and in the opinion of competent 
judges, better calculated to convey a correct and permanent 
idea to the mind, than any that have heretofore appeared. 

2. The plan of the book, and consequently the order of 
the maps, is also original. It not only gives the facts of 
the science, but it gives them in a manner admitting of 
illustration ; and in such order and connection as that they 
can hardly fail to be understood and remembered, when 
once read and illustrated. a Science," says Lord Broug- 
ham, " is knowledge systematically arranged, so as to be 



vin PREFACE. 

conveniently taught, easily learned, and readily applied." 
If this definition be correct, (and we certainly think it is,) 
it follows that it is not every book that is filled with facts 
upon a particular subject, that should be considered scien- 
tific. Quite as much depends upon the arrangement as 
upon the style of the author, or the facts themselves. 
With a view to convenience in teaching, facility in learn- 
ing, and tenacity in remembering, the matter of this 
Treatise has been arranged upon an entirely new plan ; 
and one, in the opinion of the author, more in accordance 
with the demands of philosophical classification, than some 
methods heretofore pursued. The student begins his in- 
quiries at home, or with the Solar System, and ends them 
in the more distant heavens. The Earth is considered 
where she properly belongs, namely, among the Primary 
Planets, and the Moon where she belongs, or among the 
Secondaries. Eclipses and Tides are afterwards con- 
sidered in distinct chapters, as phenomena not necessarily 
connected with a description of either the primary or se- 
condary planets. 

3. Each class of facts respecting the heavenly bodies, 
— their names, distances, magnitudes, periodic times, den- 
sity, &c. — is drawn out in brief and succinct tables, and 
arranged in Lessons in a manner well calculated to aic 
the memory, to encourage the pupil onward, and to pre- 
sent, within narrow limits, a comprehensive view of the 
whole subject. The work is written for beginners, or as a 
Text Book of Astronomy for Common Schools and Acade- 
mies; and the author has aimed less at the production of a 
profound and elaborate work, than at conciseness and practi- 
cal utility. It is believed that with this Treatise in his 
hands, and the maps spread out before him, a pupil may 
possess himself of all the leading facts of the science even 
without the aid of an instructor. It is intended to be, as 
its title imports, an " Elementary Astronomy" adapted to 
the present state of the science in this country, and to the 
wants of the public at large. Such a work, it is thought, 
has not heretofore been published. " It is seldom," says a 



PREFACE. LX 

late writer, " that men who have arrived at great distinc- 
tion in their favorite pursuit, have condescended to write a 
plain and simple treatise, suited to the wants of those who 
have just passed the threshold of science." Men who are 
conscious of superior abilities are sometimes fond of appear- 
ing learned in their productions ; and moreover, as Bake- 
well observes, i; he who attempts to make a scientific sub- 
ject familiar, runs the risk of being decried as superficial : a 
plentiful share of dullness, combined with a certain degree 
of technical precision, is regarded as essential proof of pro- 
fundity." 

4. This work is the only one before the public that con- 
tains any thing respecting the two New Planets \ namely 
Astrea, and Leverrier ; or that embodies the recent discov- 
eries of Lord Ross, respecting the Nebulae. 

5. The Book is a concise and cheap work, and conse- 
quently adapted to general circulation. The Maps can be 
purchased for schools with public moneys, so that the pur- 
chase of one of these Keys, costing the individual learner 
but a few shillings, opens the whole field, as well to the 
children of the poor, as to the more favored offspring of the 
rich. 

Such are some of the improvements upon which we 
base our claims to public patronage, in sending forth a new 
elementary work upon the subject of Astronomy. In its 
preparation for the press, the author has availed himself of 
all the helps within his reach. He has consulted all the 
books upon the subject that were available in this country, 
as well as many practical teachers, and gentlemen of ac- 
knowledged scientific abilities. But while on the one hand 
he has used books as writers generally use them, namely, 
as sources of knowledge, and has advised with men of 
learning and experience in regard to many particulars, the 
author feels bound, in justice to himself, to claim for his 
work a good degree of originality ; and to say that whether 
good or bad it is his own, and not the work of another. 

It is only necessary to add that the statistics in the 



X PREFACE. 

tables are generally given in round numbers, and accord- 
ing to what was considered the highest authorities. 

Should any errors be discovered that have escaped 
notice, they will be promptly corrected in future editions \ 
and should the work be found wanting in adaptation in 
any respect, either for city or country schools, it will at 
once undergo the requisite modifications, as we are deter- 
mined to furnish a work of the greatest possible utility, at 
the least possible expense. 

New-York, February ', 1847. 



RECOMMEADATIONS. 4 

From the Osicego Palladium. 

It is but too true that the study of Astronomy has been too much 
neglected by all classes, and especially by the youth in our common 
schools, into which the subject has rarely ever been introduced 4 owing, 
doubtless, in a great measure, to a mistaken notion (arising from the 
want of an appropriate text-book) that the subject is intricate, and a 
knowledge of it difficult to be acquired. A well digested and pro- 
perly arranged treatise on the science, therefore (such as we presume 
the one in question to be), one which will so simplify the subject as 
to render it easy of comprehension by youthful minds, will be a de- 
sideratum of no trifling importance ; and the publication of such a 
work, and its introduction into our common schools as a text-book, 
are objects deserving of encouragement and success ; and he who en- 
gages in the undertaking, will render a real service to the cause of 
education. 

We have had the pleasure of a hasty examination of the Maps 
which are to accompany this work ; and, so far as we are enabled to 
judge, they are admirably adapted to the purpose which they are in- 
tended to subserve. 



From the Northern Christian Advocate. 
***** The facts of the science are classified in a manner 
altogether original, and in our opinion well calculated to facilitate 
their acquisition, and to fasten them permanently in the mind. * 
* After an examination of the work above described, we are de- 
cidedly of opinion that it must go into very general use, where dis- 
tricts and academies will feel themselves able to purchase it. And 
yet, considering its extent and execution, the price is by no means 
disproportionate to its real worth. Though it is hardly yet from the 
press, it has already been adopted in several counties^ and com- 
mended by impartial and competent judges. 



From the Rochester Daily Advertiser. 

These Maps, with the accompanying work, seem admirably cal- 
culated to make the study of Astronomy not .only an agreeable but 
an easy one. Every school and academy in the country should be 
provided with them. 



RECOMMENDATIONS. 



From the Hon. Ira Mayhew, Superintendent of Public Instruction 
for the State of Michigan. 

Monroe, Jan. 16, 1847. 
Rev. H. Mattison ; 

Dear Sir, — The first seventy-two pages of your forthcoming 
•" Elementary Astronomy," has been received and read. Although 
1 have not seen the Maps, nor any portion of the Second Part of the 
work, yet I think it cannot fail to be eminently useful. 

Your plan is, so far as I have the means of knowing it, good and 
well executed. The manner in which you treat of the laws that 
govern the Solar Bodies seems better calculated to arrest the atten- 
tian and inform the mind of the student than any other treatise on 
that subject with which I am acquainted. 

Hoping to see the entire work soon, and wishing you success in 
the prosecution of your noble undertaking, I remain, Dear Sir, 

Yours truly 

IRA MAYHEW. 



Extract of a Letter from Prof. Smith, of the Wesley an University. 

Dr. Olin and Prof. Johnson have both expressed themselves fa- 
vorably in reference to the utility of the series of maps which you 
propose publishing. * * * Of the plan you have in view I can- 
not doubt the efficiency. Whenever instruction can be conveyed 
through the eye, that one of the external senses through which the 
impressions conveyed to the mind are the most vivid and permanent, 
it must surely be best to employ it. By the series of maps you pro- 
pose, many notions will be conveyed to the young mind which could 
hardly be communicated in any other way, and far more correct ones 
on almost all the points capable of visible illustration. Such a series 
I must therefore regard as exceedingly useful. 



From Rev. E. E. E. Bragdon, A. M., Principal of the Mexico 
Academy, Mexico, N. Y. 

Messrs. Huntington & Savage : — Having tastily examined a 
part of the work entitled " Elementary Astronomy," which is now 

1 



2 RECOMMENDATIONS. 

being issued from your press, I take pleasure in stating that I am 
much pleased with the design and execution of the work. Astro- 
nomy is confessedly a very important science, and must be regarded 
as constituting an essential part of every good educational system. 
Any work, which is calculated to elicit a more general interest in 
this interesting department of nature, and, at the same time, bring 
the study of it within the reach of all classes of community, must 
be considered highly beneficial to the cause of sound education. 
Such we regard the " Elementary Astronomy," by Rev. H. Mattison. 
It is Astronomy simplified and made plain — well adapted to the ca- 
pacities of the young. The author, having omitted the long and 
tedious mathematical demonstrations and formulas, which are essen- 
tial for those to understand who may wish to push their investiga- 
tions into the more recondite and difficult parts of the science, has 
seized upon the most interesting and important parts, and beautifully 
illustrated them by means of sixteen large and elegant maps, bring- 
ing the whole panorama of the heavens before the learner, and ren- 
dering the sublime study of Astronomy pleasing pastime. We think 
the work eminently adapted to the uses of our public schools and 
academies, and doubt not that it will secure that amount of favor 
from a discerning public which its merits may seem to demand. 

E. E. E. BRAGDON. 
Mexico, Nov.U, 1846. 

I fully concur in the above recommendation. 

JOHN SAWYER, 
Pastor of the M. E. Church, Mexico, JV. F. 



From the Faculty of Union Academy, Red Creek, N. Y. 

Union Academy, Red Creek, Nov. 17, 1846. 
Rev. H. Mattison : 

Dear Sir, — Having witnessed, last evening, an exhibition of 
your Astronomical Maps, we are fully persuaded that they are cal- 
culated to create a new and lively interest in the sublime study of 
Astronomy. They will supply a desideratum which has long been 
felt, in communicating, clearly and intelligibly, knowledge on some 
of the intricate subjects connected with this important study. 

Their introduction into our institutions of learning will greatly 
relieve the teacher, by affording important illustrations, without 
which no student can acquire a thorough understanding of the 
science. 

Please send to this Institution twenty-five copies of your " Ele- 
mentary Astronomy," and one set of your best Maps. 

HUGH B. JOLLEY, A. M., 
Principal, and Prof, of Mathematics and Astronomy. 
JOHN W. PRATT, A. M., 

Prof, of Languages. 



RECOMMENDATIONS. 3 

Report adopted by the Teachers' Institute of Orleans County, N. Y., 
Oct. 1846. 

The committee, to whom was submitted for examination the As- 
tronomical Charts of Rev. H. Mattison, ask leave to offer the fol- 
lowing report : 

In point of fitness for the popular wants on this subject, they are 
second to none within our knowledge. Among other excellencies, 
they possess the advantage over every other work of the kind, of 
combining strict accuracy with a plainness of arrangement easily 
comprehended by those least familiar with the subject ; and we do 
most confidently and cordially recommend them to the attention of 
the Trustees and Teachers of the different districts in our county, as 
worthy of introduction into every school. 

Any teacher, however unacquainted he may be with the interest- 
ing science of Astronomy, need feel no hesitancy in attempting to 
instruct a class of pupils from these Charts. Each successive step 
prepares the way for the next, in so plain and obvious a manner, as 
cannot fail- to be both interesting and instructive. They have our 
decided approbation. 

ALONZO BEEBE, Co. Sup't.A 

JAMES C. CROSS, 

CORNELL MOREY, J> Committee. 

WILLIAM ORTON, 

WM. M. MILLER, 



Resolutions of the Tompkins County Teachers* Institute, held at 
Ithaca, N. Y.,Oct. 1846. 

The undersigned, a committee appointed by the Teachers' Insti- 
tute of the County of Tompkins, for the examination of Mr. Mat- 
tison's Astronomical Maps, &c, do report as follows : 

Having examined said Maps, we consider them well calculated 
for the promotion of the science of Astronomy, inasmuch as they 
are adapted to the capacity of the youthful mind, and present to the 
understanding a familiar and well-arranged series of illustrations that 
can hardly fail to combine interest with instruction. 

S. D. CARR, 
Principal of Ithaca Academy. 
L. WETHRELL, 
Trof. of Chemistry and Mathematics. 
E. A. TOMPKINS, 
DANIEL WELLER, 
J. S. McCREA, 
J. D. THATCHER. 
Ithaca, Oct. 23, 1846. 

The above report was unanimously adopted by the Institute. 

S. ROBERTSON, Co. Sup't. 



4 RECOMMENDATIONS. 

Resolutions of the Greene County Teachers' Institute for 1846. 

At the Fall Session of the Greene County Teachers' Institute 
held in the village of Cairo, N. Y., 1846, on motion of Wm. F. 
Terhune, County Superintendent, seconded by Albert D. Wright, 
Principal, the following resolutions were unanimously adopted : 

Resolved, That the grateful thanks of the members of this In- 
stitute are due, and are sincerely tendered, to the Rev. H. Mattison, 
for his instructive illustrations and explanations of the Astronomical 
Maps of which he is the author ; that we regard those Maps as a 
valuable accession to the cause of science ; and that we heartily 
wish him entire success in the laudable efforts he is now making to 
introduce the study of the sublime science of Astronomy more ex- 
tensively in our common schools. 

Resolved, That we regard the study of Astronomy, by the ad- 
vanced scholars of our district schools, as being conducive to the im- 
provement, expansion, and elevation of their minds, enabling them 
to comprehend the stupendous machinery of nature, and impressing 
them with awe and reverence for nature's Great Architect. 

WM. F. TERHUNE, Pres't. 



From Prof. S. R. Sweet, and others, members of the Temporary 
Normal School, Redfield, N. Y. 

At a public meeting of the citizens of Redfield, and the mem- 
bers of the Temporary Normal School, convened for the purpose of 
hearing a lecture on Astronomy from the Rev. H. Mattison, the fol- 
lowing resolutions were unanimously adopted: 

Resolved, That the thanks of the citizens, and the members of 
the Institute, be tendered to the Rev. H. Mattison, for his remark- 
ably interesting and instructive lecture on the science of Astronomy. 

Resolved, That the ingeniously conceived and admirably exe- 
cuted plan of presenting the more important principles and facts 
of Astronomy to the eye, by means of outline maps, merits our 
warmest approbation and encouragement ; and as an evidence of our 
sincerity, we hereby order a set of the Maps at. once, for the public 
school in this village, and pay for them in advance. 

S. R. SWEET, Prin. Tern. N. School. 
S. BROOKS, Town Sup. 



From the Delaware Express. 

On the whole, after examining the plan of the author, and the 
Maps in particular, we do not hesitate to pronounce them of a supe- 
rior order, splendidly got up, and certainly very reasonable in price. 
We hope to hear of their introduction into the schools of our county. 



RECOMMENDATIONS. 5 

From Alexander M. Baker, Esq., County Superintendent of Oswego 
County. 

I have examined with much care Mr. Mattison's u Elementary 
Astronomy," with the accompanying Maps, and hail them as one of 
the greatest improvements of the day. Every practical school teacher 
has seen and felt the want of some elementary treatise on this sub- 
ject, that should be adapted to the capacities of children and youth ; 
and this, I think, is just the work that has long been needed ; and 
one which I hope ere long to see introduced into all our Schools and 
Academies. 

A. M. BAKER. 

Sandy Creek, Nov. 9, 1846. 



From H. A. Brewster, Esq., Chairman of the Library Committee 
of the Board of Education of the City of Rochester. 

Rochester, Oct. 30, 1846. 
Rev. H. Mattison : 

Dear Sir, — I have examined your Astronomical Maps and 
method of teaching Astronomy, with a great degree of interest, and 
am decidedly of the opinion that it is the best method yet adopted 
for giving a correct impression upon that subject to the mind of the 
young. 

The manner in which you introduce it is so simple and plain, 
that it will be easily apprehended by the smallest pupil ; and yet, 
pursuing the illustrations by the system you have adopted, he is car- 
tied regularly forward, with great facility, to a complete knowledge 
of the whole science. 

I think the Maps should be placed in all our schools and semina- 
ries of learning, and that no better use can be made of the funds ap- 
propriated by the State to educate the rising generation, than by ap- 
plying a sufficient sum to place a set in every school-house in the 
land. With great respect, your obedient servant, 

H. A. BREWSTER. 



From the Roman Citizen. 

We had the pleasure of learning from Mr. Mattison, while in 
Rome, something of the character of this publication, and would 
bespeak for it in advance the favorable attention of the friends 
of education. To public lecturers, academies, schools, and in the 
family circle, we are confident it will prove a valuable acquisition. 
This sublime and truly ennobling study is too much neglected. We 
hope to see Mr. Mattison's work generally introduced into our 
schools, being persuaded that it will do much towards rendering the 
study of Astronomy attractive and easy. 



6 RECOMMENDATIONS. 

From Rev. Eltas Bowen, D. D., of Ithaca, N. Y. 
To Messrs. Huntington & Savage, Publishers, New- York : 

From a partial examination of the work of Rev. H. Mattison, 
entitled " Elementary Astronomy," &c, with the accompanying 
Maps, and designed for common schools, I am clearly of opinion 
that it will supply a desideratum which is beginning very sensibly to 
be felt in that department of our great educational system. Passing 
over the mathematical demonstrations, or the process by which the 
truths of the science are discovered, it adapts itself to the juvenile 
mind with great readiness, by a very natural and clear embodiment 
of facts, which fall as much within the comprehension of the inci- 
pient scholar as those of common Geography. The very interesting 
and useful method of teaching by illustration is here employed, in a 
series of Maps explanatory of the phenomena of the science, with 
the happiest effect. 

ELIAS BOWEN. 

Ithaca, Oct. 22, 1846. 



From the Borne Sentinel. 

This work is eminently original, and from its utility in studying 
the science of Astronomy, we believe it will meet the approbation of 
every student, teacher, and public lecturer in the country. Mr. Mat- 
tison, the author, is learned in the science of Astronomy, and has 
for a long time applied himself with great industry in getting up this 
work. 

The plan he has adopted will furnish facilities for a thorough ac- 
quaintance with this science in the common schools of our country, 
where it has never been taught to any extent or with much profit 
and improvement to the learner. We hope to see it introduced into 
our common schools, academies, and higher institutions of learning. 



From the Genesee Evangelist. 
After giving the title of the work, the editor says : 
We have had the pleasure of examining the greater part of the 
Maps which are to accompany this work, and for correctness of de- 
sign, boldness of appearance, and simplicity and harmony of arrange- 
ment, we have never seen them excelled. They are admirably 
adapted in giving a clear and ready view of the science that they 
are designed to explain and teach. Astronomy has ever been an 
intricate study, requiring long and patient investigation. But the 
mode pursued by Rev. Mr. Mattison in teaching it, will render it 
interesting, beautiful, and inviting, and will throw a charm on every 
ascending step, exciting the mind to loftier flight, till the whole field 
is surveyed. The author has certainly rendered an essential service 
to science, and will no doubt be amply remunerated in the ready sale 
which will attend his work, and the new interest which will be im- 
parted in investigating the variety, extent, and position of the 
heavenly bodies. 



SUGGESTIONS TO TEACHERS. 



1. It is recommended that Teachers who are not familiar with 
the subject of Astronomy, should review this branch, in connection 
with the Maps. This may be done in a short time, by taking the 
book, and a map or two home with them every night. Indeed a 
teacher who has never studied Astronomy to any great extent, can 
in this way keep ahead of his school, and qualify himself in the most 
effectual manner to interest them, as they follow on and explore the 
ground over which he has so recently travelled. 

2. It is not expected that more than from fifteen to twenty min- 
utes each day can be devoted to this subject ; and the best time will 
probably be near the close of the school, as the exercise will be a 
sort of relaxation from severer studies. 

3. It is deemed of the first importance that when the time for 
studying Astronomy arrives each day, the whole school should join 
in the exercise at the same time. When one or more of the maps 
are hung up to view, and especially when the questions and answers 
upon the lessons begin, it will be found difficult to confine a scholar 
to any other study in the same room. Let every thing else then be 
laid aside for a short time each day, and let the whole school ad- 
vance together through the successive lessons. Even small scholars, 
or those who are only tolerable readers, may thus get a general 
knowledge of Astronomy, without in the least interfering with their 
Reading, Writing, Arithmetic, Geography , or Grammar. 

4. Instead of one book only in the school, as a key to the Maps, 
and that in the teachers hands, it is indispensably necessary that 
eveiy scholar pursuing the study, should have a copy of the book. 
It was in view of this necessity, thai the subject was compressed 
within narrow limits, and the book got up in the cheapest possible 
form. 

5. When the time for studying Astronomy arrives, the school 
will lay aside all other studies and take their books upon that sub- 
ject. The Teacher will inquire what Maps are necessary to illus- 
trate the lesson, to which the school will answer by naming the 
number referred to at the head of the lesson. The map, will then 
be hung up. Let the pupil understand that the left hand side of the 
map is East, the right AVest, the top North, and the bottom South. 
When, therefore, they can be hung in the south part of the school- 



Xll SUGGESTIONS TO TEACHERS. 

room, the pupil will refer every thing to the right point of compass, 
without the aid of the imagination. 

6. The Map being hung up, the school will devote some ten or 
fifteen minutes to studying the lesson, occasionally Looking at the 
map for illustration, as the thing to be learned is there pictured out. 
The oral exercise will then begin. If the lesson contains an impor- 
tant table, or list of names like lessons VII., VIII., XIV., XVIIL, 
XXL, &c, such table or list should be recited in concert. If it be 
of less moment, and withall somewhat extended, it may be passed 
by being carefully studied over, and then reviewed orally, according 
to its character, and at the discretion of the Teacher. In many 
other cases where the lessons are like those from I. to VI. inclusive, 
they should only be studied, without committing to memory ; and 
the Teacher should ascertain the knowledge thus acquired by ex- 
temporaneous questions, at the same time illustrating what may still 
appear obscure to any pupil, and correcting any mistakes into which 
individuals have fallen. 

7. After all, much will depend upon the judgment and ingenuity 
of the Teacher, and the interest he takes in the subject. Sound 
learning can never be acquired, by any mode of teaching, without 
thought and attention. Neither can any particular course be struck 
out that will be adapted to all kinds of schools, and to every part of 
the country. It will be inexpedient for the learner to pursue this 
branch at home, or in his room, except those parts of the work 
that require no illustration, or those lessons that do not refer to 
maps. In some cases, the whole subject maybe presented orally by 
the teacher, in a series of evening lectures, following the course of 
the book ; but this should rather be in addition to the regular study 
during school hours, than a substitute for it. 

With these suggestions the work is committed to the hands of 
Teachers, at the same time bespeaking their co-operation in render- 
ing it useful to the rising generation ; in detecting any errors that 
may exist ; and in making any improvements of which it may yet be 
susceptible. 



CONTENTS. 



INTRODUCTION. 

Lesson 

1. History of Astronomy, 

2. The Ptolemaic Theory, . 

3. Difficulties of the Ptolemaic Theory, 

4. The Copernican System, .... 

5. The Solar System and Sidereal Heavens, 

PART I. 

OF THE SOLAR SYSTEM. 

CHAPTER I. 

CLASSIFICATION OF THE SOLAR BODIES. 

6. Sun, Planets, Primary, Secondary, &c, 

CHAPTER II. 

OF THE PRIMARY PLANETS. 

7. Names of the Primary Planets, 

8. Distances of the Planets, 

9. Degrees, Minutes, and Seconds explained, 

10. Angular Distances, Magnitudes, &c, . 

11. The Sun as seen from different Planets, . 

12. Philosophy of the Diffusion of Light, 

13. Light and Heat of the several Planets, 

14. Magnitude of the Planets, . 

15. Relative Magnitude of the Sun and Planets, 

16. Comparative Density of ihe Planets, 

17. Attraction of the Planets, 

18. Periodic Revolutions of the Planets, 

19. Hourly Motion of the Planets in their Orbits, 

20. Centripetal and Centrifugal Forces, 

21. Diurnal Revolutions of the Planets, . 

22. True Figure of the Planets, 

23. The Ecliptic, 

24. The Poles of the Ecliptic, . 

25. Obliquitv of the Ecliptic, 

26. The Zodiac, 

27. Signs of the Zodiac, .... 



Page 
1 
2 
3 
4 
5 



8 
9 
10 
11 
12 
13 
14 
15 
15 
16 
17 
18 
19 
19 
20 
21 
22 
23 
23 
24 
24 



XIV 



CONTENTS. 



Plane of their 



Lesson 

28. Nodes — Ascending and Descending, 

29. Transits, 

30. Transits of Mercury, ...... 

31. Transits of Venus, ...... 

32. Inclination of the Orbits of the Planets to the Plane 

Ecliptic, ....... 

33. Celestial Latitude, ...... 

34. Celestial Longitude, ..... 

35. Longitude of the Ascending Nodes of the Planets, 

36. Constellations of the Zodiac, .... 

37. The Sun's Apparent Motion in the Ecliptic, . 

38. Successive Appearance of the Constellations in the 

turnal Heavens, ..... 

39. Disagreement between the Months and Signs, 

40. The Equinoxes, 

41. The Solstices, 

42. The Colures, 

43. Ellipticity of the Planets' Orbits, . 

44. Perihelion and Aphelion, 

45. Eccentricity of the Planets' Orbits, 

46. The Seasons, ...... 

47. The Sun's Declination, 

48. Right Ascension, ..... 

49 . Inclination of the Axes of the Planets to the 

respective Orbits, .... 

50. Seasons of the different Planets, " 

51. Seasons of Venus, ..... 

52. Seasons of the Earth, .... 

53. Seasons of Mars, ..... 

54. Seasons of Jupiter, .... 

55. Seasons of Saturn, ..... 

56. Conjunction and Opposition of Planets, 

57. Sidereal and Synodic Revolutions, . 

58. Elongations of a Planet, 

59. When Planets are said to be Stationary, . 

60. Direct and Retrograde Motions, . 

61. Retrograde Motions of the Exterior Planets, 

62. Venus as Morning and Evening Star, ■ 

63. Phases of Mercury and Venus, 

64. Telescopic Views of the Planets, . 

65. Of the Discovery of the several Planets, . 

66. Telescopic Views of Saturn, 

67. Dimensions, Structure, and Uses of Saturn's Rings, 

CHAPTER III. 

OF THE SECONDARY PLANETS. 

68. Character and Number of the Secondary Planets, . 
79. Supposed Satellite of Venus, .... 
70. Of the Earth's Satellite or Moon, 



of the 



Page 
25 
26 
27 

28 



Noc- 



74 
75 
75 



CONTENTS. XV 

Lesson Page 

71. Changes or Phases of the Moon, . . . * . 77 

72. The Moon's Path around the Sun, .... 78 

73. Revolution of the Moon's Nodes around the Ecliptic, . 79 

74. Sidereal and Synodic Revolution of the Moon, . . 79 

75. Revolution of the Moon upon her Axis, . . . .80 

76. Of the Moon's Librations, 80 

77. Seasons of the Moon, ....... 81 

78. Telescopic Views of the Moon, 81 

79. Physical Constitution of the Moon, Mountains, Volcanoes, 

Atmosphere, &c ........ 82 

80. Geography of the Moon, or Selenography, . , .83 

81. Moons of Jupiter, 84 

82. Satellites of Saturn 85 

83. Satellites of Herschel, 87 

84. Supposed Satellite of Leverrier's Planet, . . . .87 

CHAPTER IV. 

OF ECLIPSES. 

85. Nature and Causes of Eclipses, ..... 88 

86. Extent, Duration, and Character of Solar Eclipses, . . 90 

87. Of the Eclipses of the Moon, 94 

88. Of the Time and Frequency of Eclipses, . . . .95 

89. Eclipses, or Occultations of the Stars, .... 97 

90. Eclipses of Jupiter's Moons, ...... 98 

91. Eclipses of Saturn and Herschel, ..... 99 

CHAPTER V. 

PHILOSOPHY OF THE TIDES. 

92. Of the Nature and Causes of Tides, .... 100 

93. Lagging of the Tide — Excursions in Latitude, . . 102 

94. Spring and Neap Tides — Prof. Davies' Theory, . .103 

95. Other inequalities of the Tides, .... 107 

96. Motion of the Apsides of the Moon's orbit, . . . 109 

CHAPTER VI. 

OF C03IETS. 

97. General description of Cometary bodies, . . 110 

98. Magnitudes, Velocities, Temperature, Periods, Distances, 

Numbers, &c, of Comets. . ... 113 

CHAPTER YIL 

OF THE SUX. 

99. General Remarks respecting the Sun — its Magnitude, &c. 1 17 

100. Spots on the Sun's surface — their number, . . 118 

101. Revolution of the Sun upon his Axis, .... 118 

102. Magnitude of the Solar Spots, 119 

103. Direction, Motions, and Phases of the Solar Spots, . . 119 

104. Supposed Nature and Causes of the Solar Spots, . 121 



XVI CONTENTS. 

Lesson Page 

105. Physical Constitution of the Sun, .... 123 

] 06. The Zodiacal Light, 124 

107. Motions of the Sun in Space, . . ( . .126 

CHAPTER VIII. 

MISCELLANEOUS REMARKS UPON THE SOLAR SYSTEM. 

108. Nebular theory of the origin of the Solar System, . 127 

109. Laws of Planetary Motion, . . ' . . . 128 

110. Miniature representation of the Solar System, . . 129 

111. Were the Asteroids originally one Planet] . . . 130 

112. Are the Planets inhabited by Rational Beings'? . . 132 

PART II. 

THE SIDEREAL HEAVENS. 

CHAPTER I. 

OF CONSTELLATIONS OF STARS. 

113. Distinguishing characteristics of the Fixed Stars, . 135 

114. Classification of the Stars, 135 

115. Number of the Fixed Stars, 137 

116. Distances of the Stars, 138 

117. Magnitude of the Stars, 138 

118. List of the Constellations, 140 

119. Description of some of the Principal Constellations — 
Zodiacal Constellations, ..... . 145 

120. Northern Constellations, 147 

121. Southern Constellations, ...... 153 

CHAPTER II. 

OF DOUBLE, VARIABLE, AND TEMPORARY STARS, BINARY SYSTEMS, &C 

122. Of Double, Triple, and Multiple Stars, ... 156 

123. Of Binary, and other Systems, 157 

124. Variable or Periodical Stars, 158 

125. Temporary Stars, 159 

126. Falling or Shooting Stars, 160 

CHAPTER III. 

OF CLUSTERS OF STARS, AND NEBULA. 

127. Of Clusters of Stars, 161 

128. OfNebulse, 163 



INTRODUCTION. 



LESSON I. 

Astronomy is that science which treats of the names, 
distances, magnitudes, and motions of the heavenly bodies 
— the Sun, Moon, Planets, Comets, and Fixed Stars — and 
the laws by which they are governed. 

The oldest records of astronomical science are found 
in the Holy Scriptures. We there read of the creation, 
of the sun, moon and stars, and the commencement of 
their revolutions. In the Book of Job, which was writ- 
ten fifteen hundred years before Christ, we read of 
"Arcturus, Orion, and Pleiades " and also of "Mazza- 
roth" supposed to mean the Zodiac. It is here said, 
likewise, that the Almighty " stretcheth out the north 
over the empty place, and hangeth the earth upon 
nothing." 

The prophet Amos speaks of the " seven stars and 
Orion," seven hundred and thirty-three, years before 
Christ, and of the phenomena of day and night. 

The Greek philosopher, Pythagoras, taught astron- 
omy five hundred years before Christ, and the Egyptian 
philosopher, Ptolemy, three hundred years before the 
Christian era. His was the first regular system of as- 
tronomy. 

2 



ELEMENTARY ASTRONOMY. 



LESSON II. 



THE PTOLEMAIC THEORY. 

(Map 1.) 

The Ptolemaic System, so called from Ptolemy, 
its author, is the subject of Map No. 1. It represents 
the earth as located in the centre of the universe ; as 
being perfectly at rest ; as a plane instead of a globe ; 
and as inhabited only on one of its sides. Some sup- 
posed the earth to float upon an abyss of waters. 
Ptolemy taught, also, that the sun, moon, planets and 
stars revolved around the earth, from east to west, as 
they appear to do, every twenty-four hours. To account 
for their passing over the earth without falling down 
upon its surface, it was supposed that the heavenly bodies 
were supported by vast arches, or hollow spheres, in which 
they were firmly set like a diamond in a ring. 

But as the sun, moon, planets and stars, were not all 
at the same distance from the earth, it was supposed that 
there were several of these spheres placed one above an- 
other — that the Moon was in the first, Mercury in the 
second, Venus in the third, the Sun in the fourth, Mars 
in the fifth, Jupiter in the sixth, Saturn in the seventh, 
and the Fixed Stars in the eighth. The ancients had no 
knowledge of Herschel. 

Mercury, Venus, and the Moon, were placed in the 
three lower spheres, because they were sometimes seen 
to pass between the earth and the sun. But Mercury 
and Venus sometimes go before the sun, and sometimes 
follow after him. To account for this, it was supposed 
that besides the great circle of the heavens around which 
they passed daily, they had other smaller circles within 
their respective spheres, in which they revolved at the 
same time. These the ancients called epicycles. They 
may be seen on the Map, in the second or sphere of 
Mercury. 

To account for the rapid westward motion of these 
ponderous spheres, it was believed that the necessary 
moving power was applied in some way to the upper 



DIFFICULTIES OF THE PTOLEMAIC THEORY. 3 

sphere, above the fixed stars ; and that this sphere com- 
municated its motion to the one immediately beneath or 
within it, and so on down to the lower sphere. This, it 
was thought, moved slower than the rest, as the moon 
constantly fell back of the sun. To allow the light of 
the stars to pass down to the earth, it was supposed that 
the several concentric spheres rising one above another, 
were made of the finest crystal, and were perfectly trans- 
parent. The space above the fixed stars was designated 
as the blissful abode of departed spirits. 

On the map, the spaces between the white circles rep- 
resent the several crystaline spheres. The sun and 
moon are represented as going down in the west, the 
moon having fallen a little behind the sun, as when we 
first see the new moon; Mercury and Venus are near 
the sun, as they always are, and Jupiter, Saturn, and 
Herschel, on the left. On the right is seen a comet pass- 
ing down towards the sun. 

Such is the Ptolemaic Theory of the structure of 
the universe. 

LESSON III. 

DIFFICULTIES OF THE PTOLEMAIC THEOBY. 

(Map 1.) 

Besides the clumsiness of the machinery, it was at- 
tended by numerous difficulties which its supporters could 
never explain or obviate. 

1. It could never determine what upheld the earth. 
Rocks and mountains could not float upon water ; and if 
they could, what upheld the water ? Some imagined 
that the earth was upheld by a huge serpent, resting upon 
the back of a tortoise, as represented in the map. But 
what upheld the tortoise ? 

2. It represented many very large bodies, as the sun 
and some of the planets are now known to be, as revolv- 
ing around the earth, a comparatively small one. 

3. It adopted the most difficult and unreasonable 
plan for lighting and warming the earth, and producing 



4 ELEMENTARY ASTRONOMY. 

day and night. Taking the sun around the earth every 
twenty-four hours, was like carrying a fire around a 
person who was cold and wished to be warmed, instead 
of his turning himself to the fire as he pleased. 

4. The Ptolemaic theory would require a motion 
inconceivably rapid in all the heavenly bodies. As the 
sun is ninety-five millions of miles from the earth, the 
entire diameter of his sphere would be one hundred and 
ninety millions of miles, and its circumference about six 
hundred millions. Divide this distance by twenty-four, 
the number of hours in a day, and it gives twenty-five 
million miles an hour, or sixtv-nine thousand four hun- 
dred and forty-four miles per second, as the velocity of 
the sun ! 

This theory gives a still more rapid motion to Mars, 
Jupiter, Saturn, and the fixed stars. It would require 
the nearest of the latter to move at the rate of near four- 
teen thousand millions of miles per second, or seventy 
thousand times as swift as light, in order to accomplish 
its daily course. 

But with all these difficulties in its way, the Ptolemaic 
theory was generally believed till about the middle of 
the sixteenth century, or three hundred years ago. 



LESSON IV. 

THE COPERNICAN SYSTEM. 

(Map 2.) 

About the year 1510 Nicholaus Copernicus, of Prus- 
sia, taking some hint perhaps from the writings of Py- 
thagoras, discovered what is now generally received as 
the true theory of astronomy, and called after its author 
the Copernican System. 

The Copernican System attributes the apparent daily 
motion of the sun, moon, and stars from east to west, 
to the actual motion of the earth on its axis from west 
to east. Though the heavenly bodies seem to move, 
yet we often transfer our own motion, in imagination, to 
other bodies that are at rest ; especially when we are car- 



THE SOLAR SYSTEM AND SIDEREAL HEAVENS. 5 

ried rapidly along without effort, as in a carriage, steam- 
boat, or railway car. It places the sun in the centre of 
a system of worlds, of which the earth is one ; gives them 
a revolution around their common centre, by which the 
seasons are produced ; and another upon their axes, pro- 
ducing day and night. It accounts for all the motions of 
the heavenly bodies, and harmonizes the whole system of 
nature. 

The Coper nican System is represented in Map 2. 
In the centre is seen the sun, in a state of rest. 
Around him, at unequal distances, are the planets and 
fixed stars, the former revolving about him from west to 
east, or in the direction of the arrows. The white circles 
represent the orbits, or paths, in which the planets move 
around the sun. On the right is seen a comet plunging 
down into the system around the sun, and then departing. 
This is the Copernican Theory of the solar system. 

" O how unlike the complex works of man, 
Heaven's easy, artless, unencumbered plan." 

The truth of the Copernican theory is established 
by the most conclusive and satisfactory evidence. Eclip- 
ses of the sun and moon are calculated upon this theory, 
and astronomers are able to predict thereby their 
commencement, duration, &c, to a minute ; even hun- 
dreds of years before they occur. We shall, therefore, 
assume the truth of this system, without further proof; 
and proceed accordingly to the study of the heavenly 
bodies. 

LESSON V. 

THE SOLAR SYSTEM AND SIDEREAL HEAVENS. 

(Map 2.) 

The material universe may be divided into two parts : 
the Solar System and the Sidereal Heavens. 

The Solar System consists of the sun and all the 
planets and comets that revolve around him. 

The Sidereal Heavens embrace all those bodies that 
lie around and beyond the solar system, in the region of 
the fixed stars. 



6 ELEMENTARY ASTRONOMY. 

The relation of the one to the other may be par- 
tially understood by carefully observing Map 2. The 
sun and his attendant worlds are there seen within the 
fixed stars, which occupy the corners of the map, and 
the spaces without in every direction. If the observer 
were placed at a distance beyond the solar system, in 
any direction, he would see vast numbers of the fixed 
stars between it and him, as if they were scattered be- 
tween the eye of the learner and every part of the map. 
To us the solar system seems to be in the centre of the 
universe. 

In considering the general subject of astronomy, 
we shall divide it into two parts ; treating first of the 
Solar System, and secondly of the Sidereal Heavens, 



PAET I. 

OF THE SOLAR SYSTEM. 



CHAPTER I. 

CLASSIFICATION OF THE SOLAR BODIES. 

LESSON VI. 
(Map 2.) 

The Solar System derives its name from the Latin 
word Sol, the sun. It includes that great luminary, and 
all the worlds that revolve around him. To distinguish 
these attendant bodies from others in the heavens, they 
will be denominated Solar Bodies. 



CLASSIFICATION OF THE SOLAR BODIES. 7 

The bodies of the Solar System are divided into sev- 
eral distinct classes. 

I. The Sun is the fixed centre of the system, around 
which all the solar bodies revolve ; and from which they 
receive their light and heat. 

II. The Planets are those bodies that revolve around 
the sun, and receive their light and heat from him. The 
term 'planet signifies a wanderer, and was applied to the 
solar bodies because they seemed to move or wander 
about among the stars. In this sense comets are planets ; 
but for the sake of distinction the term is not applied to 
them in astronomy. 

1. The planets are divided into Primary and Second- 
ary planets. 

The primary planets are those larger bodies of the 
system which revolve around the sun only, as their cen- 
tre of motion. They may be distinguished in the map by 
their size, and also by their being in their orbits, or on 
the white circles. 

The secondary planets revolve not only around the 
sun, but also around the primary planets, as their atten- 
dants or moons. They may easily be distinguished on 
the map. 

2. The planets are again divided into Interior and 
Exterior planets. 

The interior planets are those whose orbits lie within 
the orbit of the earth ; or between it and the sun. 

The exterior planets are those whose orbits lie without 
the orbit of the earth. 

3. Five of the smaller primary planets are called 
Asteroids. They may be seen on the map near together, 
just above the sun. 

4. Comets are a singular class of bodies belonging to 
the solar system, distinguished by their long flaunting 
trains of light, and also by the elongated form of their 
orbits, as shown in the map. 



8 ELEMENTARY ASTRONOMY. 

CHAPTER IT. 

OF THE PRIMARY PLANETS. 
LESSON VII. 

NAMES OF THE PRIMARY PLANETS. 

(Map 2.) 

The Primary Planets are twelve in number. They 
are distinguished in astronomical books by certain cha- 
racters, which are used to represent their respective 
planets. The names of the planets and their symbols 
or signs are as follows : 

Mercury, £ C Ceres, J } 

Venus, ? < Pallas, $ > 

Earth, © ( Astrsea, * ) 

Mars, $ Jupiter, 4 

{ Vesta, g > Saturn, ^ 

( Juno, ) Herschel, *&■ 

With the exception of the Earth, Astraa, and Her- 
schel, they are all named after Heathen gods or goddess- 
es. The five enclosed in brackets are the Asteroids ; 
Mercury and Venus are the interior planets ; and Astraea 
is the new planet, or one recently discovered. These 
planets should now be looked out upon the map, and 
their comparative size, distances from the sun, and ap- 
pearances carefully noticed. 

Mercury is seen close to the sun, and directly under 
him. Venus is also near the sun, and a little above him 
on the left. The Earth is next in order, above the sun, 
and a little to the right. The Moon and her orbit will 
be seen near the earth. Mars is on the right of the sun, 
and beyond the orbit of the earth. He is the first of the 
exterior planets. Above the earth are seen the five plan- 
ets called Asteroids, viz. : Vesta, Juno, Ceres, Pallas, 
and Astrcea. Jupiter is the large planet below the sun 
on the left. His surface is striped with curious helts, and 



DISTANCES OF THE PLANETS. 9 

he is attended by four secondary planets or moons. 
Above the Asteroids on the right is seen the beautiful 
planet Saturn. He is attended by seven moons, and sur- 
rounded by two magnificent and wonderful rings. Her- 
schel and his six moons are placed on the left, near the 
upper corner of the map. 

LESSON VIII. 

DISTANCES OF THE PLANETS. 

(Map 2.) 

Map 1 shows all the planets at their relative dis- 
tances from the sun. The scale is one hundred millions 
of miles to an inch. The distances of the planets in 
miles are as follows : 



Mercury, 


37 millions. 


Ceres, 


263 millions 


Venus, 


69 


a 


Pallas, 


263 " 


Earth, 


95 


cc 


Astrsea, 


253 " 


Mars, 


145 


(C 


Jupiter, 


495 " 


Vesta, 


225 


u 


Saturn, 


900 " 


Juno, 


254 


u 


Herschel, 


1800 " 



It is almost impossible to conceive of these vast dis- 
tances. They may perhaps be better understood by con- 
sidering the time it would require for even a rapid body 
to visit them from the sun. 

Were a body to move at the rate of five hundred miles 
an hour, without intermission, it would require near eight 
and a half years for it to pass from the sun to the near- 
est of these planets. To visit the earth would require 
over twenty-one years ; and to reach Herschel over four 
hundred years ! 

Railroad cars travel at the rate of thirty miles an 
hour, or a mile every two minutes. Now if there was 
a railroad from the sun to the orbit of Herschel, and the 
orbits of the other planets w T ere stopping places on the 
route, the train would reach 

Mercury, in 152 years. 
Venus, " 264 " 
2* 



10 ELEMENTARY ASTRONOMY. 

Earth, " 361 years. 
Mars, " 554 " 
Jupiter, " 1884 " 
Saturn, " 3493 " 
Herschel, " 6933 ' " 

Such a journey would be equal to riding four hun- 
dred and fifty thousand times over Whitney's railroad, 
from Boston to Oregon. 

It is now about 5850 years since the creation of the 
world. Had a train of cars started from the sun at that 
time to visit the orbit of Herschel, and travelled day and 
night ever since, at the rate of thirty miles per hour, they 
would still have 284 millions of miles to travel before 
they could reach their journey's end. To finish the pas- 
sage would require 1083 years longer ; the whole of 
time past and a thousand years to come ! 

Such is the vast area embraced within the orbits of 
the planets, and the spaces over which the sunlight trav- 
els, to warm and enlighten its attendant worlds. 



LESSON IX. 

DEGREES, MINUTES AND SECONDS EXPLAINED. 

(Map 3.) 

In astronomy, the distances and magnitude of bodies 
are often given in degrees, minutes, and seconds. It will 
be necessary, therefore to show .what these mean. 

A circle is represented on the right in Fig. 1. 

A quadrant is the fourth part of a circle. 

A sextant is the sixth part of a circle. 

A sign is the twelfth part of a circle. 

A degree is the thirtieth part of a sign, or one three 
hundred and sixtieth part of a circle. 

A minute is a sixtieth part of a degree ; and 

A second is the sixtieth part of a minute. 

On the map the circle is divided off into parts of ten 
degrees each, and numbered in figures every thirty de- 
grees, or oftener. It will be seen that one-fourth of a 



ANGULAR DISTANCES, MAGNITUDES, ETC. 11 

circle contains just three signs, or ninety degrees; and 
half a circle six signs, or one hundred and eighty degrees. 
All circles, whether great or small have the same 
number of degrees, namely, three hundred and sixty. 
But one hundred and eighty marks the greatest possible 
angle, as a pair of compasses can be opened no farther 
than to bring the legs in a straight line. These degrees, 
&c, are used to represent the angle which any two lines 
form, coming from different points, and meeting at the 
eye in the centre. 

In the figure the lines passing from the stars on the 
left to the eye, are found by the measurement on the 
circle to be ten degrees apart. If the dotted line was 
perpendicular to the lower or plain one, they would be 
ninety degrees apart, &c. 

Degrees, minutes and seconds are denoted by certain 
characters as follows : ° denotes degrees, / denotes min- 
utes, and ;/ denotes seconds. Thus, 10° 15 y 20 /7 is read 
ten degrees, fifteen minutes, and twenty seconds. These 
characters will often be used hereafter as we proceed. 

Measurement by degrees, minutes, and seconds, is 
called angular measurement. 

LESSON X. 

ANGULAR DISTANCES, MAGNITUDES, &C 

(Map 3.) 

In Fig. 1, the observer is represented as seeing two 
stars on the left side of the map. By looking at the di- 
vided circle it will be seen that the angle which these 
two stars make at the eye is 10° ; the stars are therefore 
said to be 10° apart. If a globe filled the same angle, 
or number of degrees, as shown on the map, we should 
say it was 10° in diameter. If the space between the 
foot of a mountain and its top filled the same angle, we 
should say it was 10° high ; and if a body passed through 
the same angle, in one hour, in the dirtction of the ar- 
row, we should say its velocity was 10° an hour. 

All circles, whether large or small, have the same 



12 ELEMENTARY ASTRONOMY. 

number of degrees ; but the angle which an object 
makes at the eye will be great or small, according as it 
is near to or distant from the observer. This is illus- 
trated by fig. 2. On the left is the object. To the ob- 
server in the centre the globe is 20° in diameter ; but to 
the one on the right its diameter is but 10°. To a third 
observer, at twice the distance of the last, it would appear 
but 5° in diameter, &c. This shows why objects grow 
smaller in appearance as we recede from them, and 
larger as we advance towards them. Their apparent 
magnitude is increased or diminished in proportion to the 
distance from ivhich they are viewed. 



LESSON XI. 

THE SUN AS SEEN FROM THE DIFFERENT PLANETS. 

(Map 3.) 

By the table of distances, (Lesson VIII. ) and also by 
Map 2, it will be seen that the Sun is about twice as near to 
Mercury as he is to Venus. Of course, then, according 
to the principle illustrated in Fig. 2, his apparent diameter 
must be twice as great when viewed from Mercury as 
when viewed from Venus. From the Earth it is still 
smaller, and so on till we view him from the distant orbit 
of Herschel, from which he will appear but a small glim- 
mering point in the heavens. From the fixed star Sirius, 
he would appear smaller than Sirius appears to us. 

The relative apparent magnitude of the Sun, as seen 
from the different planets, is represented by Fig. 3. His 
angular diameter, in minutes of a degree, would be, 



l rom Mercury , 


. 82^ 


From Ceres . 11 J' 


" Venus . , 


. 44V 


" Pallas . llf 


" Earth . .. 


. 32' 


" Astrsea 12' 


" Mars . . 


. 21/ 


" Jupiter . 6' 


" Vesta . . 


. 13±' 


" Saturn . 3£' 


" Juno . . 


. 12' 


" Herschel If' 



From Mercury it is supposed that the spots on the 
Sun tfould be visible to the naked eye, as seen on the 



PHILOSOPHY OF THE DIFFUSION OF LIGHT. 13 

map ; and from Herschel the Sun himself would appear 
but as a large and brilliant star. Let the pupil imagine 
himself as approaching the sun till it has four times his 
present apparent diameter, and his spots stand out in 
full view to the naked eye ; and then let him recede from 
the sun, pass the earth and the orbits of Jupiter and Sa- 
turn, and retire away into space, till the sun appears but 
a glimmering star, and he will have some faint concep- 
tion of the almost inconceivable distances of the solar 
bodies. 



LESSON XII. 

PHILOSOPHY OF THE DIFFUSION OF LIGHT. 

(Map 3.) 

Light always moves in straight lines, unless turned 
out of its course by reflection or refraction. This is re- 
presented by fig. 4 on the map ; where the light is seen 
passing to the right, from the sun on the left. From this 
law it follows that the squares A B and C in the diagram 
would receive equal quantities of light ; but as B has 
four times, and C nine times the surface of A, a single 
square of B equal to A, would receive only one-fourth 
as much light as A ; and a square of C, equal to A, 
would receive only one-ninth as much. This difference 
in the amount of light received is caused by the unequal 
distances of the several squares from the miniature sun 
on the left. The distances are marked on the upper line 
of light by the figures 1, 2, 3. 

The rule for determining the relative amount of light 
received by several bodies, respectively, placed at une- 
qual distances from their luminary, is, that their light is 
inversely, as the squares of their distances. This rule, 
also, is illustrated by the figure. The square of 1 is 
1 ; the square of 2 is 4 ; and the square of 3 is 9. 
Hence 1, -J-, and -£, will represent their relative light, as 
already shown. The checks are designed to illustrate 
this rule. 



14 ELEMENTARY ASTRONOMY. 



LESSON XIII. 



LIGHT AND HEAT OF THE SEVERAL PLANETS. 

(Map 3.) 

By applying the foregoing rule to the planets, at their 
respective distances from the sun, we are enabled to as- 
certain the relative amount of light received by each ; 
and on the supposition that their heat is proportionate to 
their light, we can easily determine their average tem- 
perature. At the bottom of the map the planets are 
placed at their relative distances from the sun, commenc- 
ing with Mercury on the left, and ending with Herschel 
on the right. Immediately over each planet respectively, 
and near the upper line of the diagram, is marked the 
proportionate light and heat of each - , the earth being one. 
They are as follows : 

Mercury . 6£ Juno and Astrsea . *■ 

Venus . . 2 Ceres and Pallas . •£ 

Earth . . 1 Jupiter ^ 

Mars . . . £ Saturn -^ 

Vesta . . \ Herschel .... - 3 -J-j 

It appears, therefore, that Mercury has 6£ times as 
much light and heat as our globe ; and Herschel only 
g-J-g as much. Now if the average temperature of the 
earth is 50 degrees, the average temperature of Mercury 
would be 325 degrees ; and as water boils at 212, the 
temperature of Mercury must be. 113 degrees above that 
of boiling water. Venus would have an average tempera- 
ture of 100 degrees, which would be twice that of the 
earth. On the other hand, Jupiter, Saturn and Herschel 
seem doomed to the rigors of perpetual winter. Think 
of a region 27, 90, or 368 times colder than the average 
temperature of our globe. And can such worlds be in- 
habited ? If so, it must be by beings adapted to their 
abode as we are to ours. 

" Who there inhabit must have other powers, 
Juices, and veins, and sense, and life, than ours : 
One moment's cold, like theirs, would pierce the bone, 
Freeze the heart's blood, and turn us all to stone ! " 



Venus, 
Earth, 
Mars, 
Vesta, 


7,800 

8,000 

4,200 

270 


Juno, 


1,400 



RELATIVE MAGNITUDE OF THE SUN AND PLANETS. 15 



LESSON XIV. 

MAGNITUDE OF THE PLANETS. 

(Map 2.) 

In Map 2 the planets are drawn on a scale of 40,000 
miles of diameter to an inch. The sun is represented 
as but a point, because he could not be placed in the 
map, of a size proportionate to the planets. 

The diameters of the several planets are as follows : 

Mercury, 3,000 miles. Ceres, 1,600 miles. 

Pallas, 2,100 " 
Astrsea, unknown. 
Jupiter, 90,0J0 " 
Saturn, 80,000 " 
Herschel, 35,000 " 

By carefully observing each planet as laid down on 
the map, it will be seen that their relative magnitudes 
correspond with their relative diameters as here stated. 



LESSON XV. 

RELATIVE MAGNITUDE OF THE SUN AND PLANETS. 
(Map 4.) 

The relative magnitude of the sun and planets is repre- 
sented in Map 4, Fig. 1. They are all drawn on the same 
scale, as in No. 2, namely 40,000 miles of diameter 
to an inch. As the sun is 886,000 miles in diameter, he 
is drawn 22f inches across, to show his true magnitude 
as compared with the planets. These may be seen on 
the right side of the map, commencing with Mercury at 
the top, and passing downward to Herschel. 

The secondary planets will be seen around their pri- 
maries. 

The magnitudes of the primary planets as compared 
with the earth, are as follows, viz. : 



16 ELEMENTARY ASTRONOMY. 

Mercury, -f s Ceres, T -J- r 

Venus, i^o- Pallas, -^ 

Earth, 1 Astreea, unknown. 

Mars, -J- Jupiter, 1,400 

Vesta, 2"8o"y"o Saturn, 1,000 

Juno, fi§ Herschel, 90 

The sun is 1,400,000 times larger than the earth, and 
500 times larger than all the other bodies of the solar 
system put together. It would take one hundred and 
twelve such globes as our earth, if laid side by side, to 
reach across his vast diameter. 

The moon's orbit is two hundred and forty thousand 
miles from the earth. Now, if the sun was placed where 
the earth is, he would fill all the orbit of the moon, and 
ex end more than two hundred thousand miles beyond it 
on every side ! What is a globe like ours compared with 
such a vast and ponderous body as the sun ? 



LESSON XVI. 

COMPARATIVE DENSITY OF THE PLANETS. 

By density is meant compactness or closeness of parts. 
Hence we say cork is less dense than iron, and stone is 
more dense than common earth. In like manner the 
planets differ from each other in density, or in the com- 
pactness of the substances of which they are composed. 

The comparative density of the several planets, and the 
substances with which they most nearly agree in weight, 
will be shown by the following table, in which the earth 
is taken as the standard of comparison. 



Mercury, . 


. 3— lead. 


Jupiter, . 


. -J- — water. 


Venus, . . 


. -^o — earth. 


Saturn, . 


. -j^o — cork. 


Earth, . . 


. 1 


Herschel, 


. -J- — water. 


Mars, . . 


. -J 9 -,, — earth. 


Sun, . . . 


■J- — water. 



This table is one of considerable importance, and 
should be committed to memory. Its uses will be more 
clearly seen in the next lesson, 



ATTRACTION OF THE PLANETS. 17 

LESSON XVII. 

ATTRACTION OF THE PLANETS. 

Attraction or gravitation is the tendency of bodies^ to- 
wards each other. By this influence substances fall to 
the earth, when raised from it and left without support. 
The force of attraction is what constitutes the weight of 
bodies ; and its amount depends upon the quantity of 
matter in the bodies attracting, and their distances from 
each other. 

From the above law of attraction it follows that large 
bodies attract much more strongly than small ones, pro- 
vided their densities are equal, and their distances the 
same ; and as the force of attraction constitutes the weight 
of a body, it follows that a body weighing a given number 
of pounds on the Earth would weigh much more on Ju- 
piter or Saturn ; and much less on Mercury or the As- 
teroids. 

The following table shows the relative attractive force 
of the Sun and Planets. A body weighing one pound on 
the Earth would weigh, 

lbs. oz. 



)n 

a 


Mercury, 
Venus, 


ii 


Mars, 


ii 
ii 


Jupiter, 
Saturn, 


ii 


Herschel, 


ii 


The Sun, 






9i 





15 





8 


2 


8 


1 


H 





12* 


28 


5f 



A person weighing 150 lbs. on the earth, would con- 
sequently weigh 375 lbs. on Jupiter ; 4,250 lbs. on the 
sun ; and only 75 lbs. on Mars. The attractive force of 
the Asteroids is so slight that if a man of ordinary mus- 
cular strength, were transported to one of them, he might 
probably lift a hogshead of lead from its surface without 
difficulty. 

But the learner will notice that the attractive force, 
as shown in the above table, is not in strict proportion to 



18 



ELEMENTARY ASTRONOMY. 



the bulk of the planets respectively. This difference will 
be accounted for by again referring to Lesson XVI., where 
the subject of density is considered. From the principles 
there laid down it will be seen at once that though one 
planet be as large again as another, still, if it were but 
half as dense, it would contain no more matter than the 
smaller one ; and their attractive force would be equal. 
If Jupiter, for instance, were as dense as the earth, his 
attractive force would be four times what it now is ; and 
if the density of all the solar bodies was precisely the same, 
their attractive force, or the weight of bodies on their sur- 
faces, would be in exact proportion to their bulk. 



LESSON XVIII. 



PERIODIC REVOLUTIONS OF THE PLANETS. 

(Map 2.) 

It has already been stated (Lessons IV. and VI.) that 
the planets revolve around the sun. Their direction is 
from west to east, or towards that part of the heavens in 
which the sun rises. The passage of a planet from any 
particular point in its orbit, around to the same point 
again, is called its periodic revolution ; and the time oc- 
cupied in making such revolution is called its periodic 
time. 

The periodic times of the planets are as follows : 



Mercury, 

Venus, 

Earth, . 

Mars, 

Vesta, 

Juno, 

Ceres, 

Pallas, 

Astraea, . 

Jupiter, 

Saturn, . 

Herschel, 



years, 88 days. 






ec 


225 


1 


a 




1 


a 


322 


3 


u 


230 


4 


(C 


131 


4 


u 


222 


4 


C5 


222 


4 


it 


105 


11 


a 


317 


29 


u 


175 


84 


tt 





CENTRIPETAL AND CENTRIFUGAL FORCES. 



19 



The periodic time of a planet may very properly be 
called its year ; hence, one of Herschel's years would 
equal 84 of ours ;. and a year of Saturn is equal to about 
30 of ours. 

But this difference in the length of the years of the 
several planets, is not owing solely to the difference in 
the extent of their orbits : there is an actual difference in 
their velocities, as will be shown in the next lesson. 





LESSON XIX. 


RLY MOTION 


OF THE PLANETS IN THEIR OR] 




(Map 2.) 


Mercury, 


95,000 miles 


Venus, . 


. 75,000 " 


Earth, 


68,000 " 


Mars, 


. 55,000 " 


Vesta, 


44,000 " 


Juno, 


. 42,000 " 


Ceres, 


41,000 " 


Pallas, 


. 41,000 " 


Astraea, 


42,000 " 


Jupiter, . 


. 30,000 " 


Saturn, 


22,000 " 


Herschel, 


. 15,000 " 



Here, instead of finding the swiftest planets perform- 
ing the longest periodic journeys, this order is reversed, 
and they are found revolving in the smallest orbits. The 
nearer a planet is to the sun, the more rapid its motion, 
and the shorter its periodic time. The reasons for this 
difference in the velocities and periodic times of the pla- 
nets, will appear in the next lesson. 



LESSON XX. 

CENTRIPETAL AND CENTRIFUGAL FORCES. 

(Map 2.) 
The tendency of the planets towards the sun, or in 
other words, the mutual attractive force of the sun and 



20 ELEMENTARY ASTRONOMY. 

planets, is called the centripetal force ; and the projectile 
force, or that which impels the planets onward in their 
orbits, is called the centrifugal force. If the centripetal, 
or force of attraction, was suspended^ the planets would 
fly off in straight lines beyond their present orbits, and 
leave the solar system forever ; and if the centrifugal 
force was suspended, the planets would yield to the cen- 
tripetal force, and fall to the surface of the sun. 

It has already been stated, in Lesson XVIL, that the 
force of attraction depended somewhat upon the distances 
of the attracting bodies ; those nearest together being mu- 
tually attracted most. It follows, therefore, that Mercury 
has the strongest tendency towards the sun, Venus next, 
the Earth next, &c, till we get through to Herschel ; and 
as the centrifugal force, which is to balance the centripe- 
tal, is created by the velocity or projectile force of the 
planets, that velocity must needs be in proportion to their 
distances respectively, from the sun ; the nearest revolv- 
ing the most rapidly. This we find to be the actual state 
of things in the Solar System. And what wisdom and 
skill are displayed in so adjusting these great forces as 
that the planets neither fall to the sun on the one hand, 
or fly off beyond the reach of his beams on the other. As 
it is, they remain balanced in their orbits ; and steadily 
revolve at stated periods from age to age. " O Lord, how 
manifold are thy works ! in wisdom hast thou made them 
all," 

LESSON XXI. 

DIURNAL REVOLUTIONS OF THE PLANETS. 

(Map 8.) 

In addition to the motion of the planets in their orbits 
around the sun, they have another motion around their 
respective axes, producing the vicissitudes of day and 
night. So far as is known, the time of these revolutions, 
or the length of their days, respectively, is as follows : 

Mercury, ... 24 hours. 
Venus, . . . . 23i " 
Earth, .... 24 u 



TRUE FIGURE OF THE PLANETS, 21 

Mars, .... 24-i- hours. 
Jupiter, l(f " 

Saturn, . . . . 10-J- " 

Herschel, . . 1 day 18 " 

Sun, . 25 « 14 " 

The learner will not fail to observe the striking simi- 
larity in the length of the days of the first four of the 
planets ; much less the very rapid motion of Jupiter and 
Saturn upon their respective axes. As their days are 
only about five hours long, the sun must seem to mount 
very rapidly up the heavens, and to decline as rapidly 
downward to the western horizon. His progress must be 
apparent to the inhabitants of those planets. 

From the rapid rotation of Jupiter and Saturn it fol- 
lows that they must have about 875 of their days in one 
of our years ; and as Jupiter's year is about 12 times, and 
Saturn's about 30 times as long as ours, it follows that 
the former will have about 10,500 days in his year ; and 
the latter about 26,200. 

The fact that the planets revolve upon their respec- 
tive axes is ascertained by observing the motion and di- 
rection of spots on their surfaces ; or in other words, of 
their continents and seas. For instance, in observing the 
sun I discover one of his spots on his eastern limb or edge, 
and by watching it find that it passes over his disc and 
disappears from his western limb in about 12 days and 
19 hours. From this I infer that it would pass around 
and reappear where it was first seen, in 12 days and 19 
hours longer; making the time of the entire revolution 
25 days and 14 hours. It is in this way that the time of 
the revolution of the planets upon their axes is determin- 
ed. The effect of the rotation of the planets in modify- 
ing their forms, will be shown in the next lesson. 

LESSON XXII. 

TRUE FIGURE OF THE PLANETS. 

The spherical form of the planets is proof of the su- 
preme wisdom of the great Creator. Were they cubes, 



22 ELEMENTARY ASTRONOMY. 

for instance, instead of spheres, their temperature would 
be far less regular than it now is ; the sun would rise 
suddenly upon a whole side at once, and as suddenly dis- 
appear at night ; and the blessings of twilight, and the 
gradual succession of day and night, as they now trans- 
pire, would be unknown. 

On the maps the planets are represented as exactly 
round, or spherical ; but this is not their precise form. 
Their rapid motion around their respective axes has a 
tendency to depress or flatten them at their poles ; and 
extend or widen them at their equators. Hence their 
equatorial diameter is considerably greater than their po- 
lar diameter; the true figures of the planets being that 
of oblate spheroids. 

The difference between the polar and equatorial di- 
ameter of the planets respectively, so far as known, is as 
follows : 

Earth, . . 36 miles* Jupiter, . 6,000 miles. 
Mars, . . 250 " Saturn, . . 7,500 " 



LESSON XXIII. 

THE ECLIPTIC. 

(Map 5.) 

The Ecliptic is the plane or level of the earth's orbit, 
indefinitely extended. Fig. 1 represents the earth in her 
orbit, as she would appear to a beholder placed at a dis- 
tance, and elevated above the plane of the ecliptic. She 
is represented in perspective as appearing smaller as she 
grows more distant ; as keeping her poles towards the 
same points in the heavens ; and as exhibiting the ph ases 
of the moon according as we see more or less of her en- 
lightened side. She is colored green, as she usually is 
through the series, to represent her verdure. The ar- 
rows set in her orbit show her direction. 

If the pupil has any difficulty in getting a correct idea 
respecting the ecliptic, let him suppose the orbit of the 
earth to be a hoop of small wire laid upon a table : the 



OBLIQUITY OF THE ECLIPTIC. 23 

surface of the table both within and without the hoop 
would then represent the plane of the ecliptic. 

From the above definition and description it will be 
seen that the ecliptic passes through the centre of the 
earth, and the centre of the sun ; consequently the eclip- 
tic and the apparent path of the sun through the heavens 
are in the same plane. It will be easy, therefore, to as- 
certain the true position of the ecliptic in the heavens ; 
and to imagine its course among the stars on the other 
side of the globe. 

LESSON XXIV. 

THE POLES OF THE ECLIPTIC. 
(Map 6.) 

The poles of the earth are the extremities of her axis. 
The poles of the ecliptic are the extremities of the imagi- 
nary line or axis upon which the ecliptic seems to turn. 
The ends of a rod or pointer run through the map at the 
centre of the sun would exactly represent the poles of the 
ecliptic. 

As the ecliptic and equator are not in the same planes, 
their poles do not coincide, or are not in the same points 
in the heavens. 

LESSON XXV. 

OBLIQUITY OF THE ECLIPTIC. 
(Map 8.) 

It has already been stated that the sun as well as the 
earth is always in the plane of the ecliptic. But he is 
north of the equator for six months, and south six months. 
It follows, therefore, that one-half the ecliptic is south of 
the plane of the earth's equator, and the other half north 
of it. 

As the axis of the earth is inclined to the ecliptic 23° 
23', her equator must make the same angle to the eclip- 
tic in the opposite direction ; and the ecliptic must cross 



24 ELEMENTARY ASTRONOMY. 

the plane of the equator obliquely. The angle of 23° 28' 
thus made is what constitutes the obliquity of the ecliptic. 
This subject will be better understood by examining 
the figure of the earth, and the position of her equator, as 
represented on the map. 



LESSON XXVI. 

THE ZODIAC. 

(Map 5.) 

The Zodiac is a belt 16° wide, namely, 8° on each 
side of the ecliptic, and extending from west to east quite 
around the heavens. It is represented on the map by the 
plain circles above and below the ecliptic. In the hea- 
vens the Zodiac includes the sun's apparent path, and a 
space of eight degrees south and eight degrees north of it. 



LESSON XXVII. 

SIGNS OF THE ZODIAC. 

(Map 5.) 

The great circle of the Zodiac is divided into twelve 
equal parts called signs. These divisions are shown on 
the map by the spaces between the perpendicular lines 
that cross the Zodiac. The ancients imagined the stars 
of each sign to represent some animal or object, and gave 
them names accordingly. 

The names, characters and order of the twelve signs 
of the Zodiac, are as follows : 

Aries, or the Ram, . °p Libra, the Balance, . =s= 

Taurus, the Bull, . . & Scorpio, the Scorpion, . TT[ 

Gemini, the Twins, . n Saggitarius, the Archer, £ 

Cancer, the Crab, . . 25 Capricornus, the Goat, V5 5 

Leo, the Lion, . . £\ Aquarius, the Waterman, 0CC> 

Virgo, the Virgin, . . TTg Pisces, the Fishes, ... X 

The ancient astrologists supposed that each of these 
signs governed some particular part of the human body ; 



NODES — ASCENDING AND DESCENDING. 25 

and to this day people often consult the frontispiece of 
their almanacs, to see whether the sign is "in the head," 
or "in the heart; 5 ' or to attend to certain important af- 
fairs " when the sign is right." The idea seems to be 
that the word " sign " signifies an omen or prognostica- 
tion ; and that the signs of the Zodiac have some myste- 
rious control over the destiny of man. But this fragment 
of heathen astrology is fast falling into disrepute ; and 
it is hoped will soon be utterly banished from every civ- 
ilized country. 

LESSON XXVIII. 

NODES ASCENDING AND DESCENDING. 

(Map 5.) 

Fig. 1 represents an interior planet as revolving in 
an orbit inclined to the ecliptic at an angle of about 45° ; 
and as both planets revolve around the same centre of at- 
traction, the interior planet must pass through the plane of 
the ecliptic twice at every revolution : once in ascending, 
and once in descending. These two points, where the 
orbit of a planet passes through the plane of the ecliptic, 
are called the nodes of its orbit. One is called the as- 
cending, and the other the descending node. On the map 
A. N. is the ascending node, and D. N. the descending 
node. 

A line drawn from one node to the other is called the 
line of the nodes, and may be seen on the map, marked 
L. N. 

In the figure the ascending node is represented as 
being in the middle of Libra, and the descending node in 
the middle of Taurus. The design is merely to illustrate 
the subject, without representing the actual line of the 
nodes of any one of the planets. 



26 ELEMENTARY ASTRONOMY. 

LESSON XXIX. 

TRANSITS. 

(Map 5.) 

By consulting Fig. 1 it will be seen that if an interior 
planet were at her ascending node, and the earth on 
the line of the nodes, on the same side of the ecliptic, the 
planet would seem to pass over the body of the sun, as 
shown in the figure. This passage of a planet over the 
sun's disc, or between the earth and the sun, is called a 
transit. 

Mercury and Venus are the only planets that can make 
a transit visible to us ; as all the rest are exterior to the 
earth's orbit, and consequently can never come between 
the earth and the sun. But the earth may make transits 
visible from Mars, the Asteroids and Jupiter ; and they in 
turn may mak* transits for the inhabitants of all exterior 
worlds. The principle is, that each interior planet may 
make transits from all those that are exterior. 

But transits can never occur except when the interior 
planet and the earth, or planet from which the transit is 
seen, are both on the line of the nodes. The sun and 
both the planets will then be in a line, and the one near- 
est the sun will seem to pass, like a dark round spot, 
over the sun's face. 

If the orbits of Mercury and Venus lay in the plane 
of the ecliptic (see Lesson XXIII.), they would make 
transits whenever they were in conjunction with the sun. 
Even with their present inclination the same phenomenon 
would take place twice in every revolution, if Venus 
and the earth, for instance, were to start together from 
the line of Venus' nodes, and revolve in the same peri- 
odic time. Venus would then always make a transit in 
passing her nodes. 

To calculate transits at any one node we have only 
to find what number of revolutions of the interior planet 
are exactly equal to one, or any number of revolutions 
of the earth ; or in other words, when the earth and the 
planet will again meet on the line of the planet's nodes. 



TRANSITS OF MERCURY. 



27 



In the case of Mercury this ratio is as 87.969 is to 
365.256 ; from which we ascertain that 

7 periodical revolutions of the Earth are equal to 29 of Mercury ; 
13 " " " " " 54 M 

33 " " " " " 137 

46 " i( u " " 191 u 

Therefore transits of Mercury, at the same node, may 
happen at intervals of 7, 13, 33, 46, &c. years. 

All transits and eclipses are calculated upon these 
principles. 

LESSON XXX. 



TRANSITS OF MERCURY. 



(Map 5.) 

The following is a list of all the transits of Mercury 
from the time the first was observed, November 6, 1631, 
to the end of the present century. 



1631- 
1644- 
1651- 
1661- 
1664- 
1674- 
1677- 
1690- 
1697- 
1707- 
1710- 
1723- 
1736- 
1740- 
1743- 
1753- 
1756- 
1769- 



-November 6. 

-November 6. 

-November 2. 
-May 3. 

-November 4. 
-May 6. 

-November 7. 

-November 9. 

-November 2. 
-May 5. 

-November 6. 

-November 9. 

-November 10. 

-November 2. 

-November 4. 
-May 5. 

-November 6. 

-November 9. 



1776- 

1782- 
1786- 
1789- 
1799- 
1802- 
3815- 
1822- 
1832- 
1835- 
1845- 
1848- 
1861- 
1868- 
1878- 
1881- 
1891- 
1894- 



-November 2. 
-November 12. 
-May 3. 
-November 5. 
-May 7. 
-November 8. 
-November 11. 
-November 4. 
-May 5. 
-November 7. 
-May 8. 
-November 9. 
-November 11. 
-November 4. 
-May 6. 
-November 7. 
-May 9. 
-November 10. 



By carefully examining the above table it will be 
seen that the transits of Mercury all occur in the 



28 ELEMENTARY ASTRONOMY. 

months of May and November. The reason for this is, 
that his ascending node is in the 16th degree of Taurus, 
and his descending in the 16th degree of Scorpio ; the 
first of which points the earth always passes in Novem- 
ber, and the other in May. 

All the transits, therefore, that happen in November, 
are when Mercury is at his ascending node, and the re- 
sidue are when he is at his descending node. 

Again : If we take the transits in their order, as laid 
down in the table, they will be found not to occur at inter- 
vals of 7, 13, 33, 46, &c. years, as previously stated ; but 
if we take those only that occur at the same node, we shall 
find them regulated according to the ratio prescribed. 
For example : from 1631 to 1644 is 13 years ; from 
1644 to 1651 is 7 years ; from 1651 to 1664 is 13 years ; 
from 1664 to 1677 is 13 years ; from 1677 to 1690 is 13 
years; from 1690 to 1697 is 7 years, &c. Thus far 
their intervals are 7 and 13 years ; but they may hap- 
pen at the other periods. 

If we take those occurring in May we shall find them 
conforming to the same ratio ; that is, the one previously 
laid down. 

LESSON XXXI. 

TRANSITS OF VENUS. 

(Map 5.) 

8 periodical revolutions of the Earth are equal to 13 of Venus ; 
235 « " " " " 382 

243 " " " " " 346 

251 " " " <• " 408 

291 « " " « « 475 

The line of Venus' nodes lies in the middle of Gem- . 
ini and Saggitarius ; which points are passed by the earth 
in December and June. It follows, therefore, that tran- 
sits of Venus must always happen in one or the other of 
these months. 

The following is a list of all the transits of Venus 
from 1639 (the time the first was observed) to A. D. 
2012. 



INCLINATION OF THE ORBITS OF THE PLANETS. 29 



1639 — December 4. 
1761— June 5. 
1769— June 3. 

1874— December 8. 



1822 — December 6. 
2004 — June 7. 
2012— June 5. 



LESSON XXXII. 



INCLINATION OF THE ORBITS OF THE PLANETS TO THE PLANE 
OF THE ECLIPTIC. 

(Map 5.) 

Fig. 1 represents the orbit of a planet as making an 
angle with the ecliptic qf about 45°. But none of the 
planets have so great an inclination ; the main object 
here being to illustrate the subject of nodes. 

The inclination of the orbits of the several planets, 
to the plane of the ecliptic, is shown in Fig. 2. In the 
centre is seen the sun. The dotted line running hori- 
zontally across the map, and through the sun's centre, 
represents the plane of the ecliptic. On the right and 
left are seen arcs of a circle, divided off, and numbered 
every ten degrees. The plain lines, inclined more or 
less, and passing through the centre of the sun, repre- 
sent the plane of the orbits of the planets respectively. 
On the left, outside the graduated circle, the names of 
the planets are given ; and just within the circle the 
amount of the inclination of their orbits. This inclina- 
tion is as follows : 



Mercury 
Venus 
Earth 
Mars . 
Vesta 
Juno . 



70 

o 

20 

70 

130 



Ceres . 


. . 10^o 


Pallas . . 


• • 34-£° 


Astrsea . . 


7.3.0 
• • • 4. 


Jupiter . 


. . 4° 


Saturn . 


. . 2±° 


Herschel . 


40 

4 



The wide colored portion of the graduated circle shows 
the limits of the Zodiac, extending 8° each side of the 
ecliptic. 

It will be seen that the orbits of most of the planets lie 



30 ELEMENTARY ASTRONOMY. 

within the limits of the Zodiac ; but Juno, Ceres and Pal- 
las go beyond its bounds. They are therefore sometimes 
called the ultra zodiacal planets. 

Near the middle of Fig. 2 are seen two comets in their 
orbits ; one coming down from the heights North of the 
ecliptic, passing around the sun and then reascending ; 
and the other coming up from the depths South of the 
ecliptic. The design is to illustrate the fact that the 
comets do not revolve in the plane of the ecliptic, or as 
nearly so as do the planets ; but that they approach the 
sun from all directions, or from every point in the hea- 
vens. 

LESSON XXXIII. 

CELESTIAL LATITUDE. 

It will be understood by Lesson XXV., that the eclip- 
tic and equinoctial are two different planes, intercepting 
each other at an angle of 23^°. Now although terres- 
trial latitude is distance north or south of the earth's equa- 
tor, yet celestial latitude is not reckoned from the celes- 
tial equator, or equinoctial, but from the ecliptic. Celes- 
tial latitude is, therefore, distance north or south of the 
ecliptic, and as one half of the ecliptic is south of the 
earth's equator (Lesson XXV.), it follows that a star 
may be in north celestial latitude, which is, nevertheless, 
south of the equinoctial. 

LESSON XXXIV. 

CELESTIAL LONGITUDE. 

(Map 6.) 

Longitude on the earth is distance east or west from 
any given point. On all English charts and globes, it is 
reckoned from Greenwich Observatory near London ; but 
on those of American origin, it is usually reckoned from 
the meridian of Washington City. 

Longitude in the heavens is reckoned from the ver- 



LONGITUDE OF ASCENDING NODES OF THE PLANETS. 31 

rial equinox, or the first degree of Aries, eastward, around 
the ecliptic to the same point again. The map is a ver- 
tical view of the Zodiac, and when suspended to the south 
of the learner, gives a pretty correct idea of its position 
in the heavens. 

Beginning at the first point of Aries, and passing 
around the ecliptic eastward, the longitude is marked off 
on the map, and numbered every ten degrees. The en- 
tire circle, like all other circles, has 360 degrees ; which 
bring us to the point from which we started. 

From what has been said, it will be obvious that if the 
sign Aries, for instance, were directly over head, or on 
the meridian at any given time, Libra would be in the 
opposite part of the Zodiac, or in the heavens beyond the 
other side of the earth. In using longitude to show the 
position of stars or other objects in the Zodiac, we should 
say the Twins were between the 70th and 80th degrees ; 
the Lion between 130 and 140; the Balance between 
190 and 200 ; the Goat between 280 and 290, &c. The 
pupil can trace them out for himself, and mark their lon- 
gitude. 

LESSON XXXV. 

LONGITUDE OF THE ASCENDING NODES OF THE PLANETS. 

(Maps 5 and 6.) 

On Map 5, Fig. 1, the line of the nodes of the inte- 
rior planet enters the middle of Aries, and the middle of 
Libra. It was stated in Lesson XXX. that the ascend- 
ing node of Mercury was in the middle of Taurus, and 
his descending node in the middle of Scorpio. This will 
be fully illustrated by Map 6, where the line of his nodes 
is shown, and their longitude marked. The map repre- 
sents the plane of the ecliptic. This side, or north of the 
map, is called above the ecliptic, and the other side below 
the ecliptic. To pass the plane of the ecliptic, therefore, 
from south to north, is to ascend ; and to return from 
north to south is to descend. The arrows nearest the 
sun show not only the direction of Mercury, as he moves 



32 ELEMENTARY ASTRONOMY. 

in his orbit, but also his relative distance from the sun, and 
the position of his nodes in the ecliptic. The entire line 
of Venus' nodes is also laid down on the map, together 
with her distance from the sun and direction, shown by 
the arrows crossing the line. 

In astronomical tables, the longitude of the ascending 
node only is given ; for when this is ascertained, that of 
the descending node is easily inferred from it. Take for 
instance, the ascending node of Mercury. It is laid down 
on the map as in longitude 46°. Of course, then, his de- 
scending node is in the opposite side of the ecliptic, or 
just 180° distant. Add 180 to 46, and we have 226, the 
actual longitude of his descending node, as shown by the 
map. So by adding 180 to 75, the longitude of Venus' 
ascending node, we have 255, the longitude of her de- 
scending node. I have therefore given only the longitude 
of the ascending nodes of the planets, and one half the 
line of their nodes ; leaving the longitude of the descend- 
ing nodes to be ascertained in the manner already ex- 
plained. 

The longitude of the ascending nodes of the planets 
respectively, is as follows : 



Mercury . 


. 46° 


Ceres . 


. . . 80° 


Venus . . 


. 75° 


Pallas . 


. 173° 


Earth . . . 


# 


Astrsea . 


. . . 120° 


Mars . . 


. . 48° 


Jupiter. 


. . . 98° 


Vesta . . 


. 103° 


Saturn . 


. . 112° 


Juno . . . 


. 171° 


Herschel . 


. . 72° 



This subject should be well understood before the 
learner dismisses it, to enter upon the next lesson. 



LESSON XXXVI. 

CONSTELLATIONS OF THE ZODIAC. 

(Map 6.) 
By this time the reader is no doubt anxious to know 
the meaning of the strange looking figures that are placed 
around this map, in the signs of the Zodiac. It must not 



CONSTELLATIONS OF THE ZODIAC. 33 

be forgotten that a sign is merely the tic eJfih part of a cir- 
cle. The largest circle on the map is divided into signs, 
as well as into degrees. In each sign, and outside of the 
circle, is placed a picture of some kind — a bull, a lion, a 
lady with wings, a goat, or some other figure. The rea- 
son for this we will now explain. 

Outside the divided circle on the map, and around the 
different figures or pictures, may be seen numerous stars. 
Some are larger than others, and they seem to be scat- 
tered about at random. Such is the natural appearance 
of the heavens generally, in a clear night, as well that 
belt stretching over from west to east called the Zo- 
diac, as any other portion. Now the ancients imagined 
that the stars were thrown together in clusters resembling 
different objects ; and they consequently named the dif- 
ferent groups after the objects which they supposed them 
to resemble. These clusters, when thus marked out by 
the figure of some animal, person, or thing, and named 
accordingly, were called Constellations. 

As every part of the Zodiac is filled with stars, each 
sign has one or more of these ancient constellations. It 
is on this account that the figure supposed to be repre- 
sented by the constellation of each sign is still retained ; 
and the signs bear the names of their respective constel- 
lations. 

The pupil will now more clearly discover the folly of 
the idea that each sign or constellation of the Zodiac " go- 
verns " a particular portion of the human body, as stated 
in some almanacs. How preposterous the notion that a 
cluster of stars, millions of miles from our globe, govern 
a man's head, his arms, or his feet ! And yet some still 
think the "signs'' should be consulted in reference to 
many important matters. 

The names of the signs have already been given in 
Lesson XXVII., to which the learner may again turn, to 
refresh his memory, in connection with the map now be- 
fore him. 



3» 



34 ELEMENTARY ASTRONOMY. 



LESSON XXXVIL 

THE SUN'S APPARENT MOTION IN THE ECLIPTIC. 

(Maps 5 and 6.) 

In Map 5, Fig. 1, the earth is seen performing her 
annual journey around the sun. Now when the earth is 
in the sign =£= the sun will appear to be in ^ ; and as the 
earth moves on to ^1, the sun will appear to pass around 
to # . Hence, as the earth passes around in her orbit 
every year, from west to east, it is obvious that the sun 
will appear to make the circuit of the heavens in the 
same time, and in the same direction. 

All the constellations of the Zodiac seem to overtake 
and pass by the sun westward once a year ; or in other 
words, the sun appears to meet and pass through them all 
eastward, in regular order, every 365 days. 

Map 6 may illustrate this subject still more clearly. 
The sun is seen in the centre. Around the sun the earth 
is seen in her orbit, the arrows showing her direction. Now 
when the earth is in &, in November, the sun must 
seem to be in Tit, on the opposite side of the ecliptic. So 
when the earth is in rr, the sun will seem to be in } , &c. 

On the 20th of March the earth is in longitude 180, 
or in the first degree of =£= ; at which time we say the 
sun enters <p>. 

The time of the sun's entrance into the different signs 
is as follows : 



cp, March 20th. 
y, April 20th. 
n, May 21st. 
05, June 21st. 
ft, July 23d. 
TTg, August 23d. 



=£=, September 23d. 

TTL, October 23d. 

$ , November 22d. 

V5>, December 21st. 

*&, January 20th. 

X, February 19th. 



It must not be forgotten that this motion of the sun 
eastward around the Zodiac, is merely apparent ; and is 
caused altogether by the revolution of the earth around 
the sun. By following the earth in her orbit from March 



SUCCESSIVE APPEARANCE OF THE CONSTELLATIONS. 35 

20th, around to the same point again, the sun will seem 
to enter all the signs, in the order, and at the times speci- 
fied in the foregoing table. 

As we have our spring while the sun is passing 
through op, &, and n, these are called the spring signs ; 
25, £^, and tij, are the summer signs ; «q-, tt[, and $ , are 
the autumnal signs ; and y?, ~ , and }£> tne winter signs. 

This subject will be still further illustrated in the next 
lesson. 

LESSON XXXVIII. 

SUCCESSIVE APPEARANCE OF THE CONSTELLATIONS IN THE 
NOCTURNAL HEAVENS. 

(Map 6.) 

We are very apt to suppose that because we see no 
stars in the daytime, there are none in the heavens above 
us. This is an erroneous conclusion. Were it not for 
the light of the sun, the stars would shine out as brightly 
during what we now call the daytime, as they ever co 
in the night ; but instead of seeing the same constella- 
tions that we see in the night, at any given time, we 
should see those only that were visible in the night six 
months before ; and would be above the horizon again six 
months afterwards. 

The fixed stars surround the solar system in every 
direction ; and the fact that we cannot see the stars be- 
yond the sun, or in that half of the Zodiac in which he 
appears, on account of his superior light, is no proof that 
such stars do not exist and shine. When the sun is to- 
tally eclipsed the stars appear in the day time ; and if 
we look through a long tube or descend into a deep well, 
so as to shut the strong light of the sun from the eye, the 
stars may be seen even at noon in the heat of summer. 

Let this subject be illustrated by the map. 

Suppose a person to be observing the constellations of 
the Zodiac on the 21st of June. At midnight all the con- 
stellations from ^ around to op would be in sight ; but at 
twelve o'clock the next day, when the other half of the 



36 ELEMENTARY ASTRONOMY. 

Zodiac would be above the horizon, the sun would be be- 
tween the observer and the signs n and 05, and would 
shed so strong a light over the whole visible heavens, as 
to eclipse or obscure all the stars. 

But as the earth passes on in her orbit, and the sun 
seems to pass the signs eastward in regular order, the con- 
stellations will arise earlier and earlier every night ; so 
that all of them will seem to pass over from east to west 
in the night in the course of a year. 

This map may be used to show what constellations 
will be on the meridian at twelve o'clock, or at any other 
hour of the night, during every month in the year. In 
December they will be n and s ; in March rrg and ^ ; 
in June $ and y5>, &c, as the earth advances eastward 
in her orbit, and turns from west to east upon her axis. 

LESSON XXXIX. 

DISAGREEMENT BETWEEN THE MONTHS AND SIGNS. 

(Map 6.) 

The names of the months are marked around on the 
map from west to east, to show at what time the earth oc- 
cupies any particular place in her orbit ; and also when 
the sun enters the opposite sign. But the months and 
the signs do not exactly agree in longitude. The earth 
reaches long. 180°, and the sun enters op on the 20th of 
March ; so that there are eleven days of March left after 
the earth has passed into ^ and the sun has entered cp. 
Of course, then, all the months in the year are a little 
more tardy, so to speak, than the signs; and are repre- 
sented, in the map, as jutting by them eastward about 
ten degrees of longitude. 

LESSON XL. 

THE EQUINOXES. 

(Map 6.) 
The great circle of the Zodiac is divided into four 
parts, by imaginary lines running through the centre of 



THE SOLSTICES. 37 

the sun, and at right angles with each other. On the 
map they are dotted, to distinguish them from others, 
one running perpendicularly, and the other horizontally. 
The earth is represented as being at the points where 
these lines cross her orbit. 

Two of these points, namely, the upper and lower, 
are called the equinoctial points. They are so called be- 
cause when the earth is at either of them the sun shines 
perpendicularly on the equator, and consequently to each 
pole ; and the days and nights are equal all over the 
world. 

The plane of the equinoctial passes through the 
earth's equator ; or, in other words, it is the equator of 
the earth extending off into the heavens in every di- 
rection. 

The earth passes the equinoctial points on the 20th 
of March and the 23d of September ; the first of which 
is called the vernal, and the latter the autumnal equinox. 
These points being in opposite portions of the heavens, are^ 
of course, 180° apart, as appears by the map. 

LESSON XLI. 

THE SOLSTICES. 

(Map 6.) 

The dotted line running horizontally across the map 
is the line of the solstices ; and the points where this line 
crosses the earth's orbit are called the solstitial points. 

At the time of the autumnal equinox, September 23d, 
the sun is directly over the earth's equator, and his light 
extends to both poles, as shown on the map. From this 
time to December 21st, the sun declines south, till it is 
perpendicular over the tropic of Capricorn (so called 
from the sign which the sun enters on that day), when 
its southern declination is stayed or ceases. Hence the 
name solstice. 

From December 21st to March 20th the sun ap- 
proaches the equinox, which it reaches at the latter pe- 
riod, when he begins to decline northward, till on the 21st 



33 ELEMENTARY ASTRONOMY. 

of June he reaches the tropic of Cancer. He is then at 
the summer solstice. From June 21st to September 23d 
the sun again approaches the equator or equinox, at 
which time he begins again to decline south, &c. 

This declination of the sun north and south, and his 
apparent passage through the plane of the equinoctial, 
twice a year, are caused by the inclination of the axis of 
the earth to the plane of the ecliptic, and her revolution 
around the sun. What we have here said will serve 
more fully to illustrate Lesson XXV., where the obliquity 
of the ecliptic is considered. 

LESSON XLII. 

THE COLURES. 

(Map 6.) 

The Colures are two great circles crossing at the 
poles of the ecliptic (see Lesson XXIV.), and passing 
through the ecliptic at right angles. One passes through 
the equinoxes, and is thence called the Equinoctial Co- 
lure ; the other passes through the solstices, and is called 
the Solstitial Colure. They are to the heavens what four 
meridians, each 90° apart, would be to the earth. They 
divide the celestial sphere into four parts, like quartering 
an apple. Two hoops of wire, crossing between the eye 
of the learner and the sun, and also directly beyond the 
sun on the other side of the map, would represent the co- 
lures ; provided one passed through the map at the solsti- 
tial, and the other at the equinoctial points. When once 
the place of the colures is clearly ascertained, they are 
very convenient in finding particular stars or constella- 
tions either north or south of the ecliptic. 

LESSON XLIII. 

ELLIPTICITY OF THE PLANETS 5 ORBITS. 

(Map 7.) 

Thus far we have proceeded upon the supposition that 
the orbits of the planets were exact circles, and that con- 



PERIHELION AND APHELION. 39 

sequently the several planets were always at the same 
distance from the sun. It is time now to state more de- 
finitely the true figure of their orbits. 

Fig. 1 represents the earth as revolving in an ellipse, 
or oval-shaped orbit. This is its true figure ; and indeed, 
to a great extent, the figure of all the planetary orbits. 
But some are more elliptical than others, and the orbits 
of the comets, as shown in Maps 2 and 5, are more 
elliptical than those of any of the planets. 

Not only are the orbits of the planets elliptical, but 
the sun is always found one side of the centre, or nearer 
one end of the ellipse than the other, as shown on the 
map. The point where the sun is placed is called one 
of the foci of the ellipse. 



LESSON XLIV. 

PERIHELION AND APHELION. 
(Map 7.) 

When a planet or comet is in that, part of its orbit 
nearest to the sun, it is said to be at its perihelion ; and 
when at the point most distant, at its aphelion. So of the 
moon ; perigee and apogee are the points of her orbit near- 
est to and most distant from the earth. 

On the map the earth is seen at her perihelion on the 
left, and at her aphelion on the light; the two points be- 
ing at very unequal distances from the sun. In stating 
the distances of the solar bodies, we sometimes give their 
perihelion and aphelion, as well as their mean or average 
distances ; but in Lesson VIII. the mean distances only 
are given. The following table will exhibit the longitude 
of their perihelions, respectively. 



Mercury 


74° 21/ 


46^ 


Venus 


128 43 


53 


Earth 


S9 30 


5 


Mars 


332 23 


56 


Vesta 


. 249 33 


24 


Juno 


53 33 


46 



40 



ELEMENTARY ASTRONOMY. 



Ceres 


. 147° 


V 


31" 


Pallas 


. ; . 121 


7 


4 


Astraea 


135 


27 


54 


Jupiter 


11 


8 


35 


Saturn 


89 


9 


30 


Herschel 


167 


31 


16 



LESSON XLV. 



ECCENTRICITY OF THE PLANETS ORBITS. 

(Map 7.) 

The eccentricity of a planet's orbit is the distance of 
its centre from the centre of the sun. It is just half as 
great as the difference between the aphelion and perihelion 
distances. 

These principles will appear obvious by a careful ex- 
examination of Fig. 1. Place the pointer in the centre 
of the ellipse, and the sun will be found about two inches 
to the left. Of course, then, the other focus is about two 
inches to the right, or the two foci are about four inches 
apart. The difference between the earth's distance on 
the left, at her perihelion, and her distance on the right, 
at her aphelion, must therefore be four inches on the map ; 
while her eccentricity is but two inches, or just half that 
amount. 

The eccentricity of the orbits of the different planets, 
is as follows : 



Mercury 
Venus 






7,000,000 miles 
492,000 " 


Earth . 






1,618,000 " 


Mars 






13,500,000 " 


Vesta . 






21,000,000 " 


Juno 






64,000,000 " 


Ceres . 






21,000,000 " 


Pallas . 






64,250,000 " 


Astrsea . 






Unknown. 


Jupiter 






24,000,000 " 


Saturn . 






49,000,000 " 


Herschel 






85,000,000 " 



TIIE SEASONS. 41 

From the above table it appears that the orbits of Ju- 
no and Pallas are the most elliptical, while that of Venus 
is almost a circle. 



LESSON XLVI. 

THE SEASONS. 

(Map 7.) 

It has already been stated that the axis of the earth is 
inclined to the ecliptic 23° 28 7 . This is illustrated in 
Fig. 1 ; and also the fact that in consequence of the rev- 
olution of the earth around the sun, and the inclination of 
her axis to the plane of her orbit, her poles are alternately 
in the light six months, and in darkness six months. At 
the time of the equinoxes the light of the sun is seen to 
extend to both poles alike. On the 21st of June, the time 
of the summer solstice, the sun shines only to the south 
polar circle, and 23° 28 ; beyond the north pole. It is 
then summer in the northern hemisphere. At the time of 
the winter solstice this order is reversed. The sun has 
passed from over the northern tropic, across the equinoc- 
tial, to the southern tropic ; and now shines only to the 
north polar circle, and 23° 28 7 beyond the south pole. 
Thus we have the regular succession of the Seasons. 

But the map shows that we have winter in the north- 
ern hemisphere, when the earth is nearest to the sun. 
This may seem very strange to the learner, but it must 
be remembered that cold and heat in different latitudes do 
not depend so much upon the distance of the earth from 
the sun, as upon the manner in which the sun's rays strike 
her surface. Those parts of the earth upon which the rays 
of light fall perpendicularly, are always warmest ; while 
those portions upon which his beams fall obliquely, are 
comparatively cold. It is easy to see, therefore, that 
when the north pole is turned from the sun on the 21st of 
December, and the rays of light fall obliquely on the 
northern hemisphere, it will be cold, even though the 
earth may be at her perihelion ; but when the north pole is 
turned toioards the sun, on the 21st of June, the light falls 



42 ELEMENTARY ASTRONOMY. 

more directly upon the northern hemisphere, and we have 
our summer, though the earth is at her aphelion. 

The only effect of the eccentricity of the earth's orbit 
upon her temperature is, that she has probably a greater 
degree of heat during summer in the southern hemisphere, 
when the earth is at her perihelion, than we ever have at 
the north in the same latitude. But this difference must 
be very slight, if indeed it is at all perceptible. 

The subject of this lesson will be alluded to again 
when we come to consider the seasons of the other planets. 



LESSON XLVIL 

THE SUN'S DECLINATION. 

(Map 7.) 

The apparent distance of the sun north or south of 
the equator is called its declination. 

From the 20th of March to the 23d of September he 
has northern declination ; and the rest of the year south- 
ern declination. His declination is nothing at the time 
of the equinoxes ; but from that time it increases till the 
time of the solstices, when it amounts to 23£°. From 
the time of the solstices the sun gradually returns again 
towards the equator, and his declination constancy de- 
creases till he passes the equinoctial, when it again begins 
to increase, though in another hemisphere. 

The subject of this lesson is illustrated by Fig. 2 
and 3. Fig. 2 shows the position of the sun at the 
time of the equinoxes and solstices ; the manner in which 
his light strikes the earth at these times ; the zones of 
the earth ; the extent of the sun's declination, &c. 

Fig. 3 is still more full and explicit. In addition to 
what is contained in Fig. 2, it shows the place or decli- 
nation of the sun for every month in the year, and the 
manner in which his beams strike the middle of both the 
temperate zones during every successive month. Take, 
for instance, the north temperate zone, at the 45th de- 
gree of latitude. On the 21st of December, when the 



RIGHT ASCENSION, 43 

sun has the greatest southern declination, and, as shown 
in Fig. 2, shines vertically on the tropic of Capricorn, 
he would seem to be quite low down in the south, even 
at noon ; and his rays would strike the north temperate 
zone quite obliquely, as shown in the figures. From De- 
cember 21st to June 21st the sun advances towards the 
north, and the obliquity of his rays constantly diminishes. 
On the 21st of June the light falls quite obliquely on the 
southern hemisphere, where it is then winter. The two 
lines running off from the earth's surface to the letter Z, 
are designed to show the perpendicular and zenith of the 
45th degree of latitude; and also how much the sun 
lacks of being directly over head at these points, at the 
time of the solstices. 

It will be easy to see from these figures that declina- 
tion is to the heavens what latitude is to the earth. They 
may be used, also, to show the use of a quadrant, and 
the manner of determining latitude by the sun's meridian 
altitude, and his declination. 



LESSON XL VIII. 

RIGHT ASCENSION. 

(Map 6.) 

Right Ascension is distance east of the vernal equinox, 
measured on the equinoctial. 

In Lessons XXXIII. and XXXIV., it was shown that 
celestial latitude and longitude answered to terrestrial, ex- 
cept that in the former case we reckoned from and on 
the ecliptic, instead of the equinoctial. 

On the other hand, right ascension and declination 
refer directly to the equinoctial ; and consequently an- 
swer to longitude and latitude on the earth. 

The learner may here start the inquiry, Why were 
not declination and right ascension called celestial lati- 
tude and longitude, seeing that they refer to the celestial 
equator, instead of measurements from and on the ecliptic ? 
Such a question is not easily answered. The inter- 



44 ELEMENTARY ASTRONOMY. 

change of terms, as it may be called, is rather unfa- 
vorable to a ready and clear understanding of these topics. 
Even at this late period it might be a service to the sci- 
ence in the end, to call declination and right ascension 
celestial latitude and longitude. 

Right ascension is reckoned around on the equinoc- 
tial to 360°, answering to 360° of celestial longitude, 
only that one is reckoned on the equinoctial, and the other 
on the ecliptic. 

LESSON XLIX. 

INCLINATION OF THE AXES OF THE PLANETS TO THE PLANE 
OF THEIR RESPECTIVE ORBITS. 

(Map 8.) 

That the pupil may fully understand this lesson, it 
may be well to recapitulate some things already learned. 

1st. The Ecliptic is described Lesson XXIII. 

2d. The Orbits of the planets are described Lessons 
IV., XLIIL, and XLV. 

3d. The inclination of the orbits to the plane of the 
ecliptic is the subject of Lesson XXXII. 

We now call attention to the inclination of the axes 
of the several planets to the plane of their orbits. 

This is a lesson of great interest and importance; 
and although so far as the earth is concerned it has al- 
ready been anticipated, in our remarks on the seasons, 
declination, &c, still it opens a rich field of inquiry be- 
fore the student, and should receive a good degree of at- 
tention. 

On the map the dotted horizontal lines represent por- 
tions of the orbits of the planets, with the exception of 
the sun, in which case they represent the plane of the 
ecliptic. The axis of each planet is seen inclined to a 
section of its orbit at its true angle. The equators are 
shown by the double lines crossing the axes at right 
angles. The zones are distinguished by curved boundary 
lines, and by the different colors — the torrid zones being 
red, the temperate green, and the frigid white. 



SEASONS OF THE DIFFERENT PLANETS. 45 

It will readily be seen that the extent of the torrid 
zone of a planet depends altogether upon the amount of 
its polar inclination. If its axis be much inclined, as in 
the case of Venus, it will have a wide torrid zone ; but 
if its axis is but little inclined, like that of Jupiter, it will 
have a narrow torrid zone. 

The sun's declination north and south of the equator 
of each planet must be just equal to its polar inclination ; 
and as its torrid zone includes both its northern and 
southern declination, it follows that it must be twice as 
wide as the amount of its polar inclination. 

These principles will be more clearly seen by the 
following table, in which the polar inclination, greatest 
declination, and width of torrid zone, are compared : 





Inc. of axis. 


Declination. 


Torrid 


zone. 


Venus . 


. 75° 00' 


75o 00/ 


150° 


00' 


Earth . 


. 23 28 


23 28 


46 


56 


Mars . 


. 28 40 


28 40 


57 


20 


Jupiter 


..35 


3 5 


6 


10 


Saturn 


. 30 00 


30 00 


60 


00 


The Sun 


. 7 20 









Only the first part of this table need be committed to 
memory ; but the whole should be studied and compared 
with the map until its principles are fully understood. 

Of Mercury, the Asteroids, and Herschel, nothing 
definite is known respecting their polar inclination ; con- 
sequently we have no knowledge of the extent of their 
zones, or the character of their seasons. 



LESSON L. 

SEASONS OF THE DIFFERENT PLANETS. 

(Map 8.) 
The general philosophy of the seasons, together with 
the seasons of the earth, are already explained in Lesson 
XL VI. The same subject will now be resumed, as it 
relates to the rest of the planets. 



46 ELEMENTARY ASTRONOMY. 

The seasons of the planets depend upon two causes : 
the inclination of their axes to their respective orbits, 
and their periodic revolutions around the sun. The for- 
mer determines the extent of their zones, and the latter 
the length of their seasons. 

The effects of polar inclination are seen in the con- 
trast presented by Venus and Jupiter. Venus, with a 
polar inclination of 75°, has a torrid zone 150° wide ; 
while Jupiter, whose axis is inclined but 3° 5' has a 
torrid zone only 6° 10 7 wide. After the statement of 
these general principles, we shall proceed briefly to no- 
tice the seasons of the several planets. 



LESSON LL 

SEASONS OF VENUS. 

(Map 8.) 

The tropics of Venus are 75° from her equator, 
and within 15° of her poles ; and she has no frigid 
zone, or polar circles. Her periodic time being only 
225 days (Lesson XV11L), the sun passes in that 
short time from her northern solstice through her 
equinox to her southern solstice, and back to the point 
from which he started. So great is the sun's declina- 
tion on Venus, that when over one of her tropics, 
it is winter not only at the other tropic, but also at her 
equator ; and as the sun passes over from tropic to tropic 
and back again every 225 days, making spring at the 
equator as he approaches it, summer as he passes over 
it, autumn as he declines from it, and winter when he 
reaches the tropic ; it follows that at her equator Venus 
has eight seasons in one of her years ; or in 225 of our 
days. Her seasons, therefore, at her equator, consist of 
only about four weeks of our time, or 28-J- days; and 
from the heat of summer to the cold of winter can be 
only about 56 days. At her tropics she has only four 
seasons of 56 days each. 

At first view it might appear to the reader that such 



SEASONS OF MARS. 47 

an arrangement must be fatal to all vegetable life, espe- 
cially at Venus's equator ; but it should be remembered 
that He who inclined the axis of Venus to her orbit, and 
prescribed her periodic time, could as easily clothe her 
with vegetation of a month's growth, as with that requir- 
ing the lifetime of the oak or the cypress to bring it to 
maturity. 

LESSON LII. 

SEASONS OF THE EARTH. 

(Map 8.) 

It might be well here for the student to turn back to 
Lesson XLVL, and review it in connection with this map. 
Especially let him examine the figure of the earth and 
her zones with a view to the obliquity of the ecliptic, ex- 
plained in Lesson XXV. Call to mind also the subject 
of the sun's declination, Lesson XLV1L, and the differ- 
ence between referring to the ecliptic, as in celestial lati- 
tude and longitude, or to the equinoctial, as in right as- 
cension and declination. See Lessons XXXIII., XXXIV., 
XLVIL, and XL VIII. 

LESSON LIII. 

SEASONS OF MARS. 

(Map 8.) 

The polar inclination and zones of Mars are very 
similar to those of the earth ; but owing to the difference 
of his periodic time, his seasons are very different from 
ours. His year of 687 days is divided into four seasons 
of about 172 days each, or nearly twice the length of the 
seasons of the earth. 

His polar inclination is 5° 12 7 greater than that of the 
earth ; making his torrid zone wider, and his polar circles 
greater than ours; while his temperate zones are some- 
what narrower. 



48 ELEMENTARY ASTRONOMY. 



LESSON LIV. 

SEASONS OF JUPITER. 

(Map 8.) 

So slight is the inclination of Jupiter's axis to his or- 
bit, that it affords him but a very narrow torrid zone. 
The inclination of his orbit to the ecliptic is but 1° 15 7 , 
and his axis is inclined to his orbit but 3° 5 7 ; so that his 
axis is nearly perpendicular to the ecliptic. The sun 
never departs more than 3° 5 y from his equator, and still, 
as his periodic time is about 12 years (Lesson XVIII.), 
he has alternately six years of northern and six of south- 
ern declination. His narrow torrid zone and small polar 
circles leave very extensive temperate zones. In pass- 
ing from his equator to his poles, we meet every variety 
of climate, from the warmest to the coldest, with but slight 
variations in any latitude, from age to age. His days and 
nights are always nearly of the same length, as the sun 
is always near his equinoctial. His poles have, alter- 
nately, six years day and six years night. 

In connection with the above facts, it may be well to 
associate the amount of light received by this planet; his 
magnitude ; his oblate figure ; his rapid rotation upon 
his axis ; and his distance from the sun. The pupil can- 
not too often call up the facts already learned, as he ad- 
vances from lesson to lesson. In this way he will soon 
be able to state the most interesting particulars respecting 
each of the solar bodies. 



LESSON LV. 

SEASONS OF SATURN. 

(Map 8.) 

The polar inclination and zones of Saturn differ but 
little from those of Mars ; but his seasons are greatly 
modified by the length of his periodic time. This being 
about 30 years, his four seasons must each be about 7£ 



SEASONS OF SATURN. 49 

years long ; and his pclar regions must have, alternately, 
15 years day, and 15 years night. 

The rings of Saturn, which lie in the plane of his 
equator, and revolve every 10^ hours, are crossed by the 
sun when he crosses the equinoctial of the planet. Du- 
ring the southern declination of the sun, which lasts fifteen 
years, the south side of the rings is enlightened, and has 
its summer. It has also its day and night, by revolving 
in a portion of the planet's shadow. 

When the sun is at the southern tropic, it is midsum- 
mer on the south side of the rings ; as the rays of light 
then fall most directly upon them. As the sun approach- 
es the equator, the temperature decreases, till he crosses 
the equinoctial, and the long winter of fifteen years be- 
gins. At the same time the north side of the rings be- 
gins to have its spring ; summer ensues, and in turn it 
has fifteen years of light and heat. 

Of the seasons of Saturn, and the structure, dimen- 
sions, and uses of his wonderful rings, we shall remark 
further hereafter in a distinct lesson, in connection with 
Map 11. 

Before dismissing the subject of the Seasons, we wish 
to add a remark or two applying the facts we have just 
been considering, to an argument which is sometimes met 
with in the pulpit, and in theological works. The ex- 
tremes of cold and heat in different zones on the earth 
are cited as proofs of the Divine displeasure, and conse- 
quently of the natural depravity of man. A scientific 
text-book is no place to obtrude private theological views 
upon the public, hence we have no opinion to express here 
respecting the doctrine referred to ; but it must be obvi- 
ous to the reader that there are greater extremes of cold 
and heat on some other worlds than on our own ; conse- 
quently whatever is inferred from such a state of things 
on our globe, respecting the moral condition of her inhab- 
itants, should be inferred respecting every other planet 
whose seasons are known. But if we are not prepared 
to say that all the planetary worlds are inhabited by fall- 
en and guilty beings, we must conclude that however true 
the doctrine of natural depravity may be, the above 

4 



50 ELEMENTARY ASTRONOMY. 

argument is fallacious ; and ought never to be advanced 
in its support. True science and religion always go 
hand in hand; and a bad argument is always injurious 
to a good cause. 

LESSON LVI. 

CONJUNCTIONS AND OPPOSITION OF PLANETS. 

(Map 9 ) 

When any two or more of the solar bodies are found 
in the same longitude, they are said to be in conjunction. 
Fig. 1 represents the Sun in the centre, and Venus, the 
Earth, and Mars, at different points in their orbits. If the 
Earth was at D, and Venus at I or S, she would be in con- 
junction with the Sun, both appearing to be in the point 
between tf and n, or according to Map 6, in the 60th de- 
gree of longitude. 

The interior planets have two conjunctions ; the infe- 
rior conjunction, when between the earth and the sun, as 
at I; and the superior conjunction, when be\ond the 
sun, as at S. At the superior conjunction the enlighten- 
ed side of the planet is towards the earth ; and at her in- 
ferior, the dark side. 

When at her superior conjunction, Venus is 154 mil- 
lions of miles from the earth ; but when at her inferior 
conjunction, she is only 26 millions of miles distant. The 
reason for this great difference will be seen by a glance 
at the map ; which shows her the whole diameter of her 
orbit farther off when at S than at I. 

The exterior planets have a superior conjunction, as 
Mars at N ; but they can never get between the earth 
and the sun to form an inferior conjunction. When, 
therefore, a planet gets in the same longitude as the earth, 
like Mars at F, it is said to be in opposition. 

A planet in conjunction rises and sets nearly with the 
sun ; but one in opposition rises when he sets, and sets 
when he rises. 

Lesson XXXII. shows the orbit of Venus to be inclined 
to that of the earth in an angle of 3 ' 2 ° ; hence as one half of 



SIDEREAL AND SYNODIC REVOLUTIONS. 51 

her orbit is above the ecliptic, and the other half below, 
she will always appear either above or below the sun when 
in conjunction, except when she is at one of her nodes ; 
in which case she will appear to pass over the sun's disc, 
as represented in the figure. See Lesson XXXI. 



LESSON LVII. 

SIDEREAL AND SYNODIC REVOLUTIONS. 
(Map 9.) 

The sidereal or periodic revolution of a planet is its 
passage from any particular point in its orbit, around to 
the same point again. 

A synodic revolution is one extending from either an 
inferior or superior conjunction to the same conjunction 
again. It is therefore considerably more than one com- 
plete revolution around the sun. 

For example : were the earth stationary at D, the su- 
perior conjunction of Venus would happen 112-J days af- 
ter her inferior conjunction ; or in just half her periodic 
time ; but as both are in motion in the same direction, one 
revolving in 365 days, and the other in 225, it is obvious 
than when Venus reaches the point I. the earth will be 
far behind ; and when the earth reaches D, Venus will 
have advanced to M in her second round ; and will then 
have to overtake the earth before an inferior conjunction 
can be effected. This will occur when the earth reaches 
the point L in her second round. 

From one inferior conjunction to another is 594 days ; 
requiring about 2f revolutions of Venus, and nearly 
If revolutions of the earth. 

The periodic times of the planets were given in Les- 
son XVIII. ; but for the sake of a better understanding of 
the subject, the sidereal and synodic periods will here be 
given in connection. They are as follows: 

Sidereal. Synodic. 

Mercury . . 83 days. . 115 days. 

Venus . . 225 " . 584 " 

Earth . . 365 " . 365 " 



52 ELEMENTARY ASTRONOMY. 



Mars 


1 year- 


-322 


clays. 


780 days. 


Vesta 


3" 


u 


230 


a 


503 " 


Juno 


4 


iC 


131 


ee 


474 " 


Ceres 


4 


a 


222 


a 


466 " 


Pallas . 


4 


i( 


222 


it 


466 " 


Astrsea . 


4 


u 


105 


a 


476 " 


Jupiter . 


11 


i( 


3L7 


a 


399 " 


Saturn . 


29 


u 


175 


a 


378 " 


Herschel 


84 


ii 


— _ 


a 


369-}- " 



This is an interesting table, and may be studied for 
some time by the more advanced student to great advan- 
tage. He may imagine Mercury hurrying round to his 
starting point in 88 days, and in 27 more overtaking the 
earth, even before she has performed one-third of her an- 
nual journey. 

The periodic time of Mars being nearly double that of 
the earth, her synodic period is but little over two years. 
By subtracting the earth's period from the synodic period 
of the rest of the planets, the remainder will show how 
long the earth is in overtaking the exterior planets re- 
spectively, after she has completed one revolution. Thus, 
the synodic time of Vesta is 503 days. In 365 days the 
earth completes one revolution, and reaches the point from 
which she set out. Vesta is then 365 days ahead of the 
earth, but moving at a four years' pace ; so that in 138 
days the earth overtakes her, and they are again in con- 
junction. In the cases of Jupiter, Saturn, and Herschel, it 
requires still less time. Their periods are long, and they 
move slowly in longitude ; so that when the earth has 
completed a period, they are but a short distance in ad- 
vance, or to the east of her, and she soon overtakes them. 
By subtracting, it will be seen that the time required is, 
for Jupiter, 34 days; for Saturn, 13 days; and for Her- 
schel only 4£ days. Map 2 might be serviceable in il- 
lustrating this subject, so far as relates to the exterior 
planets. 

The learner must not forget that the exterior planets 
have but one conjunction, while the interior have two ; 
and that in the preceding table the time is given from one 



WHEN PLANETS ARE SAID TO BE STATIONARY. 53 

conjunction to another of the same hind. The opposite 
conjunction occurs in just half the synodic period. 



LESSON LVIII. 

ELONGATIONS OF A PLANET. 

(Map 9.) 

The elongation of an interior planet is its angular 
distance east or west of the sun, according as it follows 
or precedes him. The greatest elongation of Venus is 
48°, and that of Mercury only 29°. 

But these alternate elongations east and west are not 
always the same. Those of Mercury vary from 16° 12' 
to 28° 48 ; ; while those of Venus vary much less. E 
and W mark the positions of Venus at the time of her 
greatest elongation. 

From the above facts several other important facts 
are deduced. The first is, that the orbits of Mercury and 
Venus are within that of the earth. If it were not so, 
they would depart farther from the sun, and sometimes 
appear in opposition to that luminary. In the second 
place, they show that the orbit of Mercury is within that 
of Venus ; otherwise his elongation would exceed that 
of Venus. Thirdly, they show the ellipticity of the or- 
bits of Mercury and Venus. If their orbits were com- 
plete circles their greatest elongation would elways be 
the same ; but as it varies, it proves that they are not 
always at the same actual distance from the sun, or, in 
other words, that their orbits are more or less elliptical. 



LESSON LIX. 

WHEN PLANETS ARE SAID TO BE STATIONARY. 

(Map 9.) 

For a short time, while at or near their greatest elon- 
gation, the interior planets seem neither to recede from, 
or approach towards, the sun. They are then said to 



54 ELEMENTARY ASTRONOMY. 

be stationary* These periods are just before and just 
after an inferior conjunction. They are represented, in 
Fig. 1 at E and W. At E the planet would be com- 
ing towards the earth, and at W going from it. 



LESSON LX. 

DIRECT AND RETROGRADE MOTIONS. 

(Map 9.) 

It was stated in Lesson XVIII., that the planets re- 
volved in their orbits from west to east, or in the order of 
the signs. But they do not always appear to maintain 
this order. At times they advance regularly through 
the signs, and again retrace their course. Hence the 
distinction of direct and retrograde motions. Direct mo- 
tion is from west to east ; retrograde is from east to west. 

The general course of the planets is eastward, their 
retrogression being but for a short time, when the direct 
course is again resumed. 

The cause of this seeming irregularity will appear by 
again consulting Fig. 1. The signs will be seen marked 
°P, tf > n> &c., on the right and left sides of the map, 
and may be imagined around the whole figure. When 
Venus is at W, she would seem, to an observer on the 
earth, to be in }£> m tne signs of the upper figure. As 
she passed* on in the direction of the arrows, from W to 
E, her motion would be direct, and she would seem to 
pass through ^ ? y n , s , and into Q ; but in passing 
from E to W she would seem to fall back through 05. n, 
&c. These are her direct and retrograde motions. 

But the amount of apparent retrogression is greatly 
reduced by the motion of the earth in the same direction ; 
as for instance, if the earth advances only from D to the 
lower hand (O^T 3 ), during a revolution of Venus, she 
would not retrograde beyond the beginning of 05. 

The above principles are as applicable to Mercury as 
to Venus. 



RETROGRADE MOTIONS OF THE EXTERIOR PLANETS. 55 



LESSON LXI. 

RETROGRADE MOTIONS OF THE EXTERIOR PLANETS. 

(Map 9.) 

The apparent retrogression of the exterior planets is 
effected in a manner somewhat different from that of the 
interior planets. 

Suppose the earth at A, and Mars at B ; he would be 
seen among the stars at C. As the earth gains upon 
Mars, and reaches the point D, Mars, being at F, would be 
seen at G, or west of where he was first seen. When 
the earth reaches II, and Mars is only at J, he will be 
seen at K ; or some 15° back, or west, of his first appa- 
rent position. 

The part of the great circle of the heavens through 
which a planet seems to retrograde, is called its arc of 
retrogradation. In the figure it is the arc of the circle 
between C and K. 

The following table will show the arc of retrograde 
motion, and also the time of retrogression in days. 

Arc. Days. 

Mercury .... V&%° 23 

Venus 16 42 

Earth 

Mars 16 73 

Vesta 13 83 

Juno 12 99 

Ceres 12 99 

Pallas 12 99 

Astrsea 12 99 

Jupiter 10 121 

Saturn 6 139 

Herschel .... 4 151 

Here it may be interesting to observe, that the more 
distant the exterior planet the less its arc of retrograda- 
tion, and the longer its lime. The reason for this may 
be illustrated by the map, Fig. 1. Suppose Mars at F 
to represent Herschel. Now as his year consists of 



56 ELEMENTARY ASTRONOMY. 

eighty-four of our years, it follows that the earth would 
pass him eighty-three times during one of his revolu- 
tions ; and that during a revolution of the earth he would 
pass through only -^ part of his orbit; or about 8^°. 
The planet F would thence seem to retrograde slowly on 
the ecliptic nearly half the year ; or while the earth was 
passing from A to H on the map. 

Another result which may be seen in the table is, 
that the more distant the planet is from the earth's orbit, 
the smaller the angle which will be necessary to include 
that orbit ; and the less the arc of retrogradation de- 
scribed by the planet on the concave of the heavens. 
But I must not explain and illustrate too much, lest the 
learner find no chance to think for himself. 



LESSON LXII. 

VENUS AS MORNING AND EVENING STAR. 

(Map 9.) 

" Next Mercury, Venus runs her larger round, 
With softer beams and milder glory crown'd ; 
Friend to mankind, she glitters from afar, 
Now the bright evening, now the morning star. 
From realms remote she darts her pleasing ray, 
Now leading on, now closing up the day ; 
Term'd Phosphor when her morning beams she yields, 
And Hesp'rus when her ray the evening gilds. 

It has been seen that in making her revolutions, Venus 
is sometimes east and sometimes west of the sun. From 
her inferior to her superior conjunction she is west of the 
sun ; and from her superior to her inferior conjunction 
east of him. Now it is obvious that when she is west of 
the sun she will go down before him, and cannot be seen 
in the west after sunset ; but if she sets before the sun 
she will rise before him, and can be seen in the east be- 
fore sunrise. When, therefore, Venus is west of the sun 
she is morning star. When she is east of the sun she 
rises after the sun, and may be seen above the horizon in 
the west, after the sun is set. She is then evening star. 



PHASES OF MERCURY AND VENUS, 57 

The ancients supposed these were two different stars, 
calling the first Phosj)Jwr, and the other Hesperus. 
Venus is alternately one or the other about 292 days. 
For 146 after her inferior conjunction she lingers farther 
and farther behind the sun, in the west, till she reaches 
her greatest eastern elongation. She then seems to ap- 
proach the sun again for 146 days, when she passes her 
inferior conjunction, and becomes morning star. After 
this she rises more and more in advance of the sun for 
146 days, when, having reached her greatest ivestern 
elongation, she begins to fall back again towards the sun, 
and in 146 days is at her superior conjunction. This 
passed, she is again evening star. 

Fig. 2 is designed fully to illustrate all that may yet 
seem obscure to the learner. From W to E will repre- 
sent her direct motion, in the order of the signs. From 
E around to W again shows her retrograde motion. S 
and I mark her superior and inferior conjunctions ; and 
the appearance of a transit is represented on the sun's 
disc. 

By imagining the sun and Venus, as represented in 
the figure, to rise in the east and pass over to the west, 
the student will see that if Venus were at W she 
would be morning star, and at her greatest elongation ; 
but if at E she would be evening star, &c. It would be 
a useful exercise to observe the exact position of Venus 
in the heavens, at the time of studying these lessons, and 
then point out that position on the map. 

LESSON LXIII. 

PHASES OF MERCURY AND VENUS. 

(Map 9.) 

As Mercury and Venus are opaque bodies, like our 
earth, only those portions of their surface appear bright 
which are enlightened by the sun ; and as their enlight- 
ened sides are turned towards us, little by little, they pre- 
sent, when seen through a telescope, all the different ap- 
pearances or phases of the moon. 

4* 



58 ELEMENTARY ASTRONOMY. 

Fig. 2 represents Venus in her orbit, and exhibiting 
all her different phases, in the course of her revolution. 
At I, her inferior conjunction, her dark side is towards us, 
and her enlightened side invisible. As she passes from 
I to W, and so on round to S, we see more and more of 
her enlightened side, till her whole illuminated disc is in 
view. From her superior to her inferior conjunction she 
continues to wane, till her dark side is again turned di- 
rectly towards the earth. 

Although when at S, her whole enlightened hemi- 
sphere is towards the earth, still she is less brilliant than 
when at E and W ; owing to her increased distance from 
us, and her being, apparently, in the neighborhood of the 
sun. 

It will be seen that Venus is the whole diameter of 
her orbit nearer to us, at her inferior conjunction, than at 
her superior ; and as her mean distance from the sun is 
69 millions of miles, her distance from the earth must va- 
ry to the extent of twice that amount, or the whole diam- 
eter of her orbit, which is 138 millions of miles. It is 
not strange, therefore, that her apparent magnitude un- 
dergoes sensible variations between her conjunctions. 



LESSON LXIV. 

TELESCOPIC VIEWS OF THE PLANETS. 

(Map 10.) 

Although in the preceding lessons we have frequently 
alluded to the appearance of some of the planets, when 
seen through a telescope, it is thought important to de- 
scribe those appearances more in detail ; and to illustrate 
the descriptions by appropriate engravings. This is the 
object of Map 10. 

Before any particular planet is noticed, it may be well 
to state a few general facts respecting these primary 
bodies. 

1. They all have the same general figure, namely, 
that of spheres or spheroids. 



TELESCOPIC VIEWS OF THE PLANETS. 59 

2. They all seem to be surrounded by an atmosphere, 
of greater or less density and extent. 

3. The spots or belts seen upon their surfaces from 
time to time, by different observers, seem to be in the 
main permanent, and indicative of large divisions of land 
and water, like our continents and seas. 

With these preliminaries, they will now be taken up 
and considered in order. 



MERCURY. 

11 Of Mercury,* 5 says Dr. Herschel, "we can see little 
more than that it is round, and exhibits phases. It is too 
small, and too much lost in the neighborhood of the sun, 
to allow us to make out more of its character." But 
this is not the opinion of every observer, Mr. Schroeter, 
an eminent German astronomer, assures us that he has 
not only seen spots on the surface of Mercury, but also 
mountains, the height of two of which he actually mea- 
sured. They were situated in the southern hemisphere 
of the planet, and the highest was found to be nearly 
eleven miles in height. 

Numbers 1 and 2 on the map, are representations of 
Mercury. The spots supposed to have been seen by 
Schroeter, are represented on his disc, and he has a faint 
bluish tint as when seen through a telescope. As else- 
where stated he exhibits the different phases of the moon 
during his synodic journey around the sun. 

VENUS. 

The figures from 3 to 12 inclusive, are telescopic 
views of Venus. As a whole they represent her various 
phases, as already explained in Lesson LXIII. ; and il- 
lustrated by the lower figures of Map 9. Figures 3, 4, 
11 and 12, show her horned, as when near her inferior 
conjunction. Figures 5 and 10 show her as she ap- 
pears when at her greatest elongation ; 6 and 9 as gib- 
bous, between her greatest elongation and superior con- 
junction ; and 7 and 8 as she appears at her superior 
conjunction. 



60 ELEMENTARY ASTRONOMY. 

But these ten views present a great variety as it 
respects the spots that appear upon the surface of the 
planet. They seem not only to vary inform but also in 
their number. It may be proper, therefore, to state that 
these views were not all enjoyed by any one person, or 
during the same period of time. 

Fig. 3 is a view by Schroeter, in 1791. 

Fig. 4 " Bianchini, in 1726. 

Fig. 5 • " Cassini, in 1667. 

Fig. 6 " " in 1666. 

Figures 7 and 8 represent the face of the planet, as it 
is supposed she would have appeared, at the time of 
some of the other views, had her whole hemisphere been 
enlightened. It will be seen that each of these figures 
combine two other views. 

Fig. 9 is a view by Schroeter, in 1790. 

Fig. 10 is a view often had by the celebrated Dr. Dick. 

Figures 11 and 12 are repetitions of former views, 
with the crescent inverted, in order to illustrate the sub- 
ject of Venus's phases. 

The surface of Venus is variegated with mountains, 
some of which are estimated to be over twenty miles in 
height. Three elevations have been estimated at lOf, 
1\\ and 19 miles, respectively. 

The atmosphere of Venus is supposed to surround her 
to the depth of only about three miles ; but it is supposed 
to be very dense. 

The color of Venus is a silvery white. When at her 
greatest elongation, she is sufficiently bright to cause a 
perceptible shadow if her light is intercepted. 

THE EARTH. 

That the learner may know the grounds of the infer- 
ences drawn from the telescopic appearances of the pla- 
nets, in regard to their geography, or their great natural 
divisions, as continents, seas, &c, we present him at 
No. 13 with a telescopic view of the planet Earth. Let 
him imagine himself to be placed upon Mercury, for in- 
stance with a good telescope, observing our planet. At 



TELESCOPIC VIEWS OF THE PLANETS. 61 

the time of her opposition she would appear full from 
Mercury. The continents and islands would appear 
brighter than the rest of her disc ; as they would reflect 
a stronger light than oceans, seas, and lakes. By watch- 
ing these spots they would be found to cross the earth's 
disc in 12 hours, from which the observer would infer 
that our globe revolved on her axis in 24 hours, and from 
the direction of the spots he would deduce the inclination 
of her axis to the plane of her orbit, &c. 

From the passage of clouds over her surface, and other 
phenomena, it would be inferred that the Earth had an 
atmosphere, and the different zones, and the changes of 
the seasons, might present a variety of colors to the celes- 
tial observer. 

To a person on one of the exterior planets, the Earth 
would present all the phases of the Moon. The study of 
geography has no doubt made the learner familiar with 
the figures under consideration ; but if he can divest him- 
self for a moment of all particular knowledge of our 
globe, and contemplate her from a distance, as a planet, 
with what new interest does it invest her ! She not only 
becomes one of a class, from which we may reason analo- 
gically respecting the physical constitutions and design of 
other worlds ; but while we look with wonder upon the 
planetary orbs, and long to know more of their physical 
structure, we look upon the earth as the only orb which 
we are allowed to visit, and with whose history and pecu- 
liarities we may now become acquainted. And as the 
student looks upon the whole Western hemisphere, let 
him exclaim, "What is man /" What is a city, an empire, 
or a world, in the great universe of the Almighty ? 



MARS. 

The figures from 14 to 23 inclusive are representa- 
tions of Mars. The first two, namely 14 and 15, are 
views by Cassini, as long ago as 1610. They are copied 
from a volume of the Transactions of the Royal Society 
of London. Figures 16 and 17 represent views had by 
Maraldi, a celebrated French astronomer, in 1704. Figs. 



62 ELEMENTARY ASTRONOMY. 

18 and 19 represent the appearance of the spots on 
Mars, as seen by Dr. Hook in 1666, from a drawing made 
at the time by him. Figures 20 and 21 represent views 
by Sir William Herschel, previous to 1784. Fig. 22 is 
a view by Sir John Herschel, as copied by Nichol in his 
" Solar System," and by several other astronomical wri- 
ters. Fig. 23 is a view by Dr. Dick, in 1832, and also 
in 1837. It is copied, as several of the above are, from 
his " Celestial Scenery." 

It may seem impossible to the learner that all this 
variety in appearance could be produced by permanent 
objects on the surface of the planets ; but let him remem- 
ber that the map of Mars, which he is studying, is drawn 
upon a sphere ; and that the revolutions of a planet would 
necessarily produce a constant change, not only in the 
general appearance, but also in the apparent form of the 
spots. 

The bright spot on ihe upper end of Fig. 22, at the 
planet's north pole, is supposed to be the reflection of 
light from snow and ice. This supposition is rendered 
probable by the fact that the spot disappears as the north 
pole of the planet is turned towards the sun, and returns 
again with the departure of the direct rays of the sun, 
and the return of winter. 

The surface of Mars is variegated with oceans, seas, 
and continents, with mountains and vales, like all the 
rest of the planetary bodies. "On this planet," says Dr. 
Herschel, " we discern, with perfect distinctness, the out- 
lines of what may be continents and seas." The celebra- 
ted Madler, of Berlin, constructed a complete map of the 
surface of Mars, with accurate delineations of its great 
natural divisions, as one would draw an outline map of 
the world from an artificial globe. 

The color of Mars is red, owing, it is supposed, to the 
density of his atmosphere, which may color the whole 
scene, as clouds put on a gorg ous crimson in the morn- 
ing or evening sky. This color is not merely telescopic : 
it is the natural color of the planet as seen by the naked 
eye ; and by it he may easily be distinguished from the 
fixed stars. 



TELESCOPIC VIEWS OF THE PLANETS. 63 



THE ASTEROIDS. 

Of the Asteroids very little is known, on account of 
their distance and their diminutive size. A thin haze, or 
nebulous envelope, has been observed around Pallas, sup- 
posed to indicate an extensive atmosphere ; but no spots 
or other phenomena have ever been detected. It is hoped 
that if ever Lord Rosse returns from examining the distant 
nebulae, he will give us some new light respecting the 
bodies of the Solar System. 

The Asteroids are never visible to the naked eye. 
Through a telescope they have a pale ash color, with the 
exception of Ceres, which in color resembles Mars. 

JUPITER. 

Fig. 24 is a representation of Jupiter, the prince of 
planets. His natural color is a palish yellow. His belts 
are seen where they are usually found, namely, on each 
side of his equator, or in his temperate zones. The map 
shows his oblate form, or the difference between his polar 
and equatorial diameter. 

What the belts of Jupiter are is uncertain. " They 
are generally supposed to be nothing more than atmos- 
pherical phenomena, resulting from, or combined with, the 
rapid motion of the planet upon its axis." In number they 
vary from one to eight. Sometimes they continue with- 
out change for months, and at other times break up and 
change their forms in a few hours. Dark spots are also 
frequently seen in these belts, one of which was known 
to maintain the same position for upwards of forty years. 

SATURN. 

Fig. 25 is a telescopic view of Saturn with his belts 
and rings. The belts resemble those of Jupiter, already 
described. His rings will be noticed in a subsequent 
lesson, in connection with Map 11, to which the reader is 
referred. The body of Saturn is of a lead color — the 
rings a silvery white. 



64 ELEMENTARY ASTRONOMY. 



HERSCHEL. 

Upon this distant orb' no spots have ever yet been dis- 
covered. It is supposed (probably from analogy) to be 
surrounded by an atmosphere ; but even this is not cer- 
tain. Through a telescope " we see nothing but a small, 
round, uniformly illuminated disc, without rings, belts, 
or discernible spots." It is of a pale ash color. 



LESSON LXV. 

OF THE DISCOVERY OF THE SEVERAL PLANETS. 

Mercury, Venus, Mars, Jupiter, and Saturn, have 
been known from the earliest ages in which astronomy 
has been cultivated. 

Ceres was discovered by Piazzi, at Palermo, Jan. 1st, 
1801. 

Pallas was discovered by Dr. Olbers, of Bremen, 
March 28th, 1802. 

Juno was discovered by Mr. Harding, Sept. 1st, 1804. 

Vesta was discovered by Dr. Olbers, March 29th, 
1807. 

Astraza was discovered by Mr. Henche, of Dresden, 
Dec. 15th, 1845. 

Herschel was discovered by Sir William Herschel, 
March 13th, 1781. 

Le Verrier's Planet. — Since the preceding lessons 
were written, a New Planet has been added to the list of 
those previously known, by the discovery of Dr. Galle, 
of Berlin. That our readers may the better appreciate 
this wonderful achievement of science, we copy the fol- 
lowing letters from the London Times, in which this inte- 
resting subject is considered at length. 

THE NEW PLANET. 

Esh, near Durham, Oct. 8, 1846. 
But a few months have elapsed since the discovery 
of the small planet Astrcea, the companion of the small 



DISCOVERY OF LE VERRIER's PLANET. 65 

planets Juno, Ceres, Pallas, and Vesta, already known. 
The last few days have brought us the intelligence of the 
discovery of another new planet, under circumstances so 
unexampled, as to form the most brilliant achievement of 
theoretical and practical astronomy. Some of your read- 
ers may be interested in a familiar explanation of the steps 
which have led to this interesting discovery. 

The motions of all the planets are affected by the gra- 
vitation of the planets to one another ; and the places of 
the planets in the heavens are computed beforehand, so 
that the positions given by observation can be constantly 
compared with those previously calculated. Now the ob- 
served motions of the planet Uranus, the most distant 
hitherto known in our system, when thus compared, were 
found not to agree with the motions which the planet 
would have, after allowing for the influence of all the 
known planets, and when it was found that the deviations 
were far greater than any which could be ascribed to 
mere errors of observation, that they were of a regular 
character, and of such a nature as would arise from the 
action of a still more distant planet, the attention of astro- 
nomers was directed to ascertain whether the disturbances 
w T ere such as to point out the position of the disturbing 
planet. As long ago as the year 1842, a communication 
took place between Sir John Herschel and the lamented Ger- 
man astronomer, Bessel, on this subject: and there is rea- 
son to suppose that some researches on the subject will be 
found among Bessel's papers; for, in a letter written Nov. 
14, 1842, to Sir J. Herschel, Bessel says, " In reference to 
our conversation at Collingwood, I announce to you that 
Uranus is not forgotten." The question was, however, 
taken up by other astronomers. Le Verrier, in France, 
and Mr. Adams, of St. John's College, Cambridge, in Eng- 
land, each in ignorance of each other's labors, proceeded 
to investigate this most intricate question, and arrived in- 
dependently at the same conclusion, that the probable 
place of the suspected planet was about 325° of heliocen- 
tric longitude. This was sufficient to point out, within 
certain limits, the part of the heavens at which the pla- 
net, if visible, would be seen ; and, in consequence, Pro- 



66 ELEMENTARY ASTRONOMY. 

fessor Cballis, at Cambridge, for the last two months, wag 
engaged in mapping the neighboring stars with a view of 
detecting the planet. Sir John Herschel alluded to the 
probability that the planet would be detected in the speech 
which he made on resigning the chair at the late meeting 
of the British Association. Having observed that the last 
twelvemonth has given another new planet to our system, 
he added, " It has done more. It has given us the pro- 
bable prospect of the discovery of another. We see it as 
Columbus saw America from the shores of Spain. Its 
movements have been felt, trembling along the far-reach- 
ing line of our analysis, with a certainty hardly inferior 
to that of ocular demonstration." 

The eloquent and glowing anticipation of the future 
was soon to receive its accomplishment. On the 31st of 
August, Le Verrier made public the following elements 
of the orbit of the supposed planet, deduced by most la- 
borious calculations from the observed disturbances : 



Semiaxis major 


• 


36,154 




Eccentricity 


. 


0,10761 




Longitude of Pei 


rihelion 


2*4° 45/ 




Mean long. Jan. 


1, 1847 


318° 47/ 




Periodic time . 


. 


217,387 sidereal 


years. 


Mass . 


. 


— JL _ 
3 9 U 





He also announced that the planet would probably 
present a disc of about 3 7/ in*magnitude. This announce- 
ment reached Dr. Galle, at Berlin, on the 23d of Septem- 
ber, and on the same evening Dr. Galle, on comparing 
the stars in Dr. Bremiker's chart with the heavens, found 
a star of the eighth magnitude which was not marked up- 
on the map. The place of this star was accurately ob- 
served, and on comparing this place with its position on 
the following night, its motion, amounting to about 4° in 
right ascension, and 30 y in declination, was detected ; and 
the star was proved to be the expected new planet. 

It ought to be noticed that the new investigations of Le 
Verrier, accompanied with a recommendation to astrono- 
mers to search for the planet by examining whether any 
star presented a sensible disc, did not reach Cambridge 



DISCOVERY OF LE VERRIER's PLANET. 67 

till September 29, and that Professor Challis, on that very 
evening, singled out one star, as seeming to have a disc, 
and that star was the planet. Thus the theory, derived 
by a most abstruse calculation, from long continued ac- 
curate observation, has been completely verified ; and a 
triumph has been gained which will go down to posterity 
among the most brilliant of astronomical discoveries. 

The known boundaries of our planetary system have 
thus been nearly doubled ; a planet is added to it requir- 
ing more than 217 years to complete its revolution round 
the sun ; and moving in regions so remote as to receive 
but fgVoth part of the light and heat which our earth 
enjoys. _ 

It will remain to be discovered whether, as seems most 
probable, this planet is accompanied with a train of at- 
tendant satellites ; whether its motions are in accordance 
with the known laws of gravitation ; or whether it, in 
turn, is to serve as the means of a still further extension 
of the solar system. 

There is one circumstance connected with this new 
planet which is too remarkable to be overlooked. It was 
long since noticed by Bode, that the distance of the plan- 
ets from the sun follows a peculiar law, which may be 
thus stated — that if the distance of Mercury from the sun 
is assumed to be 4, the distance of Venus, the next planet, 
is 3 added to 4, or 7 ; that of the earth, which is next, 
twice 3 added to 4, or 10 ; and thus for the remaining 
planets, the distances from each other are doubled every 
time, as may be seen from the following table : 



7 3 

10 6 



Name of Planet. D;st. from the Sun. Difference. 

Mercury ... 4 3 
Venus . 
Earth 

Mars .... 16 12 

Small Planets 28 24 

Jupiter .... 52 48 

Saturn . . . 100 96 

Uranus . . . 196 192 
New Planet . . 388 



68 ELEMENTARY ASTRONOMY. 

The distance of the new planet then approximately 
satisfies this very remarkable law ; and the little stranger 
is at once recognized as bearing a strong family likeness 
to the other members of our system. 

The new planet was observed at Durham observatory 
Oct. 3, and Oct. 6 ; and the following results obtained : 

Greenwich mean time. R. A. Greenwich mean time. H. D. D. 

Oct. 3 8.48 21.52.31.07 

Oct. 6 11.88 .20.92 Oct. 6 11.25.6 103.28.55.1 

TEMPLE CHEVALLIER. 

Probable discovery of a ring to the new planet : 

Starfield, Liverpool, Oct. 12. 

On the 3d instant, whilst viewing this object with my 
large equatorial, during bright moonlight, and through a 
muddy and tremulous sky, I suspected the existence of a 
ring round the planet ; and on surveying it again for some 
time on Saturday evening last, in the absence of the moon, 
and under better, though still not very favorable atmos- 
pherical circumstances, my suspicion was so strongly 
confirmed of the reality of the ring, as well as of the ex- 
istence of an accompanying satellite, that I am induced 
to request you, as early as possible, to put the observa- 
tions before the public. 

The telescope used is an cquatorially mounted New- 
tonian reflector, of 20 feet focus, and 24 inches aperture, 
and the powers used were various, from 316 to 567. At 
about 8f hours, mean time, I observed the planet to have 
apparently a very obliquely situated ring, the major axis 
being seven or eight times the length of the minor, and 
having a direction nearly at right angles to a parallel of 
declination. At the distance of about three diameters of 
the disc of the planet, northwards, and not far from the 
plane of the ring, but a little following it, was situate a 
minute star, having every appearance of a satellite. I 
observed the planet again about two hours later, and no- 
ticed the same appearances, but the altitude had then de- 
clined so much that they were not so obvious. My im- 
pression certainly was that the supposed satellite had 
somewhat approached, but I cannot positively assert it. 



TELESCOPIC VIEWS OF SATURN. ' 69 

With respect to the existence of the ring, I am not able 
absolutely to declare it, but I received so many impres- 
sions of it, always in the same form and direction, and 
with all the different magnifying powers, that I feel a very 
strong persuasion that nothing but a finer state of atmos- 
phere is necessary to enable me to verify the discovery. 
Of the existence of the star, having every aspect of a sa- 
tellite, there is not the shadow of a doubt. 

Afterwards I turned the telescope to the Georgium 
Sidus, and remarked that the brightest two of his satel- 
lites were both obviously brighter than this small star ac- 
companying Le Verrier's planet. 

WM. LASSELL. 

In the periodical from which we copy, this statement 
of Mr. Lassell is accompanied by a drawing, represent- 
ing the appearance of the planet as above described. 

From the calculation submitted in the foregoing ac- 
counts it appears that the Le Verrier planet must be near- 
ly four thousand millions of miles from the sun ! Verily, 
such a discovery is "enlarging the boundaries of the So- 
lar System " most effectually. But what is this distance 
after all, when we consider that it would require more 
than 5000 such journeys to reach the nearest of the fixed 
stars ? 

LESSON LXVI. 

TELESCOPIC VIEWS OF SATURN. 

(Map 11.) 

Before the invention of the Telescope, Saturn was 
known only as a distant planet, devoid of that special in- 
terest with which modern discoveries have invested him. 
But since the powers of that wonderful instrument have 
been brought to bear upon him, he has assumed new and 
resplendent glories, and now stands forth to view as one 
of the most interesting objects in the gorgeous heavens. 

Though we have no room in this treatise to describe 
the different kinds of telescopes, or to detail their history, 



70 ELEMENTARY ASTRONOMY. 

we propose, nevertheless, to give some idea of its improve- 
ment, by tracing the successive steps by which we have 
arrived at our present knowledge of the planet Saturn. 

The objects arranged across the top of the map are 
representations of a variety of telescopic views of Saturn, 
by different observers, during the period of 45 years; or 
from 1610 to 1655. Though not arranged in the order 
we intended, each separate view may probably be iden- 
tified by the learner, with proper care and attention. Let 
it be understood, then, that the figures 1, 2, 3, &c, over 
the top, refer to two views each, viz., the two immediately 
under and each side of them. In this manner I shall pro- 
ceed to consider them. 

But it may be well here to observe, that these differ- 
ent appearances of Saturn were owing almost solely to 
the imperfect state of the telescope at those early periods 
of its history. 

The view presented at the right of Fig. 1, was had by 
Galileo, the inventor of the telescope, in 1610. The 
other, on the left, was by Scheiner, in 1614. The right 
figure, near No. 2, represents a view by Riccioli in 1640, 
and the left one a view by Helvetius in 1643. In 1649, 
the same observer saw Saturn as represented on the right 
of Fig. 3, and in 1650 as he is seen on the left. The lat- 
ter was a very excellent view for that early period. In 
the same year, however, he had a still better view, as re- 
presented on the right of Fig. 4. On the left, near the 
same figure, is a view by Riccioli in 1651. The re- 
maining four may be taken in the order in which they oc- 
cur on the map. They were all had in 1655, the first by 
Fontani ; the second by Divini ; the third by Riccioli ; 
and the fourth by Gassendus. 

The real appearance of Saturn, as seen through a 
common and cheap telescope, is well represented at A or 
B, immediately under the above views, with the exception 
of the opening between the rings. We have often seen 
him as here represented, — and with the belts across his 
disc as shown in Map 10, — and that too with an ordinary 
refracting telescope ; but in earlier periods in the history 
of the science, such views were denied even to the most 
wealthy, devoted, and profound astronomers. 



TELESCOPIC VIEWS OF SATURN. 71 

But this wonderful planet does not present the same 
appearance at all times, even with the aid of the hest glass- 
es. Indeed, the better the instrument the more percepti- 
ble his variations. In the course of 30 years, the time of 
his periodic revolution, he presents all the different phases 
shown at Fig. 3, from A to H. At one time the rings 
are entirely invisible, except as a dark stripe across the 
body of the planet, as seen at A. About 3| years after- 
wards the rings appear slightly opened, as at B ; and in 
3 1 years more they appear as at C, &c. 

These different phases are all accounted for by Fig. 2. 
Here the sun is seen in his place in the centre, and the 
earth and Saturn in their orbits, as they may be supposed 
to appear to a beholder at a distance, and elevated some- 
what above the plane of the ecliptic. This diagram may 
be used to illustrate a variety of principles. 

1. It shows how the axis of Saturn (as well as that of 
the Earth, &c.) preserves its 'parallelism in all parts of its 
orbit, and from age to age. 

2. It illustrates the subject of his seasons, as partially 
explained in Lesson LV. ; and shows how the sun must 
shine on one side of his rings 15 years, and on the other 
15 years. At A the light falls directly on the edge of the 
rings ; but as soon as he passes that equinoctial point, the 
sun shines upon the lower or southern side of the rings, 
and continues to do so till the planet reaches its other 
equinox at E. Here the light crosses over to the upper 
or north side of the rings, upon which it continues for the 
next 15 years ; or till the planet passes round to A again. 

3. It shows that Equinoxes and Solstices are by no 
means peculiar to the earth — they belong to all the plan- 
etary bodies, in the figure, A and E are the equinoc- 
tial, and C and G the solsliiial points. 

4. The learner should test himself by this figure to 
see if he fully understands the subject of the sun : s decli- 
nation, as explained in Lesson XLVII. 

5. As before said, this view of Saturn in his orbit ac- 
counts for all his different phases during his periodic jour- 
ney, as shown at Fig. 3. Let the student suppose him- 
self on the earth, where he really is, and watching Sa- 



72 ELEMENTARY ASTRONOMY. 

turn in his course ; and he will find that the rings must 
necessarily present all the variety in appearance which 
is seen in Fig. 3, as well as every intermediate degree of 
contraction and expansion. 

Let this explanation be traced through. Take any 
particular position of Saturn, or take them in order, begin- 
ning at A, and it will be found that the view denoted by 
the corresponding letter in Fig. 3 must be the appearance 
from the earth, as she comes round between Saturn and 
the sun. At C the rings are thrown up, and hide the up- 
per edge of the planet ; while at G they seem inclined 
the other way, and the planet hides the upper edge of 
the rings, (fee. 

6. This diagram shows why we cannot see Saturn at 
all times in the year. Suppose him to be at C, for in- 
stance, on the first of January, and the earth on the same 
side of her orbit ; of course he would be directly over- 
head, or rather on the meridian, at midnight, and might 
therefore easily be seen for six hours preceding, and six 
following that hour. In six months from that time, or by 
the first of July, the earth will have passed around to the 
point opposite G ; but as Saturn has moved but a short 
distance apparently in his orbit, he will not only be 
above the horizon in the daytime, but he will be nearly in 
conjunction with the sun. He must therefore be invisi- 
ble till the earth again gets around where Saturn will be 
comparatively in opposition, or on the dark side of the 
earth. 

LESSON LXVII. 

DIMENSIONS, STRUCTURES, AND USES OF SATURN'S RINGS. 

(Map 11.) 

Diameter of the planet . . 80,000 miles. 

Distance to the interior ring . . 20,000 " 

Width of the interior ring . . 20,000 " 

Opening between the rings . . 2,000 " 

Width of the exterior ring . . 10,000 " 

External diameter of the outer ring 192,000 " 

Thickness of the rin^s . . 100 " 



DIMENSIONS, ETC., OF SATURN^ RINGS. 73 

Fig. 4 on the map is a vertical view of the rings of 
Saturn, or such as an observer would have if he were 
situated directly over either pole of the planet, and at a 
considerable distance from it. The opening between the 
rings, and between the planet and the rings would then 
be visible all around, and of uniform width. Through 
these openings the stars would be as distinct as in any 
other portion of the celestial sphere ; hence we have so 
represented in the figure. 

Fig. 5 is a view of the rings as they would appear to 
an observer situated upon the body of the planet itself, 
and about half way from his equator to his north pole. 
This is a summer view, of course, as the rings are en- 
lightened ; whereas during winter in the northern hemi- 
sphere the rings would look dark, like the dark part of 
a new moon. 

Under this gorgeous arch may be seen a portion of 
the planet's surface. On the right is a new moon, and 
on the left a full moon, both in view at the same time, one 
in the west and the other in the east. On the left, and 
crossing the rings, may be seen the shadow of Saturn, 
gradually ascending the arch as the night advances, till 
it reaches the zenith at midnight, and disappears in the 
west at the approach of day. 

Fig. 6 is a similar view from the body of Saturn, the 
observer being located at a distance from the equator, or 
near his pole. The arch would then appear low down in 
the south, and also more narrow and slender ; and a much 
smaller portion of the rings would appear above the ho- 
rizon. The following particulars may conclude this in- 
teresting lesson. 

1. By observing the motion of certain spots or ine- 
qualities in the rings of Saturn, it has been ascertained 
that they revolve around the planet in 10-J- hours ; or in 
the time of his diurnal revolution (Lesson XXL). 

2. That the rings are solid matter, like the body of 
Saturn, seems evident from the fact that they reflect the 
light of the sun very strongly, and cast a deep shadow up- 
on the planet's surface. 

3. Stars have sometimes been seen between the in- 

5 



74 ELEMENTARY ASTRONOMY. 

ner and outer rings, which proves them to be actually 
separated. 

4. Of the uses of these wonderful rings it is sufficient 
to say that they serve as so many reflectors to the planet ; 
and being only about ^ part as distant as our Moon, 
and of such vast magnitude, they must tend greatly to 
modify the climate of the planet, by contributing to the 
light and heat of his summer evenings. During the 
winter in each hemisphere, the rings cast a shadow, and 
increase the intensity of the cold. 



CHAPTER III. 

OF THE SECONDARY PLANETS. 
LESSON LXVIII. 

CHARACTER AND NUMBER OF THE SECONDARY PLANETS. 

(Map 2.) 

The secondary planets are those comparatively small 
bodies that accompany the primaries in their course, and 
revolve around them. As the primaries revolve around 
the sun, so the secondaries revolve around their primaries. 

The number of secondary planets positively known 
to exist is eighteen. Of these, the Earth has one, Jupi- 
ter four, Saturn seven, and Herschel six. They may be 
seen on the map at their relative distances from their 
primaries. Their relative magnitudes are also repre- 
sented. 

Though the secondary planets have a compound mo- 
tion, and revolve both around the sun and around their 
respective primaries, they are subject to the same general 
laws of gravitation — of centripetal and centrifugal force 
— by which their primaries are governed. Like them, 
they receive their light and heat from the sun, and re- 
volve periodically in their orbits, and on their respective 
axes. In the economy of nature they seem to serve as 



OF THE EARTH'S SATELLITE OR MOON. 75 

so many mirrors to reflect the sun's light upon superior 
worlds, when their sides are turned away from a more 
direct illumination. The secondary planets are gener- 
ally called moons, or satellites. 



LESSON LXIX. 

SUPPOSED SATELLITE OF VENUS. 

Several astronomers have maintained that Venus is 
attended by a satellite. From the observations of Cas- 
sini, Mr. Short, Montaigne, and others, as quoted by Dr. 
Dick,* it seems highly probable that such a body exists. 
M. Lambert supposed its period to be 11 days, 5 hours, 
and 13 minutes ; the inclination of its orbit to the eclip- 
tic 63f ° ; its distance from Venus about 260,000 miles ; 
and its magnitude about % that of Venus. It is to be 
hoped that this interesting question will ere long be fully 
settled, as it is one which numerous telescopes, both in 
this country and in Europe, have capacity to decide. It 
is a question worthy of the attention of Lord Rosse, and 
the powers of his colossal reflector. 



LESSON LXX. 

OF THE EARTH'S SATELLITE OR MOON. 

(Map 12 ) 
To ordinary observers of the heavens, the Moon is an 
object of great interest. Her nearness to the earth — her 
magnitude — her rapid angular motion eastward — her per- 
petual phases or changes, and the mottled appearance of 
her surface, even to the naked eye, all conspire to arrest 
the attention, and to awaken inquiry. Add to this her 
connection with Eclipses, and her influence in the produc- 
tion of Tides (of both of which we shall speak hereafter 

* Celestial Scenery, pp. 84—89. 



?o 7000.000 

_JL. 

1 3 



76 ELEMENTARY ASTRONOMY. 

in distinct chapters), and she opens before us one of the 
most interesting fields of astronomical research. 

The following table exhibits the principal statistics 
and facts respecting the Moon, and should be carefully 
studied or committed to memory. 

Mean distance from the earth's centre 240,000 miles. 
Sidereal revolution . . . 27| days. 

Synodic revolution . . . 29-^ " 

Periodic revolutions per year, nearly 13 
Direction in orbit, from west to east. 
Hourly motion in orbit . . . 2,300 miles. 

Mean angular motion per day 13° 10 7 35 7/ 
Diameter ..... 2,160 miles. 
Apparent angular diameter . 31' l n 

Bulk, as compared with the earth 
Bulk, " " " the sun . 

Surface, as compared with the earth 
Density, the earth being 1 | 

Inclination of orbit to the ecliptic . 5° 9 7 
Excentricity of orbit . . . 13,333 miles. 

Longitude of ascending node . . variable. 

Inclination of axis to orbit . . . 1^° 

Revolution upon axis . . . . 29 J days. 
Light reflected by her, as compared with 

that of the sun .... ^ m 

By comparing the distance of the Moon, as expressed 
in the foregoing table, w T ith that of the Sun, (Lesson 
VIII.) it will be seen that the latter is four hundred times 
as far off as the former. It is for this reason that she 
generally appears as large as the Sun, when in fact he is 
seventy million times the largest. The Moon may there- 
fore well be regarded as our near terrestrial neighbor. 

It may also be interesting to compare the angular 
magnitude of the Moon as seen from the earth, with that 
of the Sun, as given in Lesson XI. They seem to differ 
but 53 /7 ; or less than one minute of a degree. Thus the 
Sun, on account of his immense distance, looks no larger 
than the moon ; when in fact he is equal in bulk to sev- 
enty millions of such bodies. 



CHANGES OR PHASES OF THE MOON. 77 

If the pupil does not fully understand the cause of 
this agreement in the apparent magnitude of the Sun and 
Moon, when they are in reality so disproportionate in 
bulk, let him turn back and review Lesson X., and the 
map and figure therein referred to. 

LESSON LXXI. 

CHANGES OR PHASES OF THE MOON. 

(Map 12.) 

The upper row of figures on the map represents the 
changes of the moon in passing from new to full moon, 
and around to new moon again. The first figure on the 
right represents the new moon, when, if visible at all, we 
see only her dark side. She is then at her conjunction, 
or in the same longitude with the sun, and to ordinary 
observers is invisible. As she advances eastward in her 
orbit, she falls behind the sun in his apparent daily 
course, and in a few days is seen in the west just after 
sundown, in the form of a slender crescent, as seen in the 
next view to the left. As she advances, we see more and 
more of her bright side, as represented on the map, till 
she reaches her opposition, when her enlightened hemi- 
sphere is towards us, and we see her as a full moon. 

From this time onward the ivest side of the moon be- 
gins to be obscured, for want of the sun-light, and the 
crescent begins to be inverted. From the first quarter to 
the full, and from full moon to the last quarter, the moon 
is said to be gibbous. 

The cause of these changes is further illustrated in 
Figure 2, where the Earth is shown in the centre, and 
the Moon at various points in her orbit. The sun is 
supposed to be on the right, as in Figure 3. The out- 
side suit of moons shows that in fact just one half of the 
moon is always enlightened ; while those on the inside 
show how much and ichich part of her enlightened side is 
visible from the earth. A is the new moon. B shows her 
when first visible. C is the first quarter ; D gibbous ; E 
full moon • F gibbous ; G last quarter ; H the crescent 



78 ELEMENTARY ASTRONOMY. 

inverted ; and A new moon again. This revolution of 
the moon around the earth, is called a lunation. 

The points A and E, in the moon's orbit, are called 
her syzygies ; C and G her quadratures ; and B, D, F, 
and H, her octants. 



LESSON LXXII. 

THE MOON'S PATH AROUND THE SUN. 

(Map 12.) 

The Moon has two centres of motion viz., the Earth 
and the Sun. She may therefore be said to have a sort 
of compound orbit. Were the earth at rest, the moon's 
path around her would be comparatively uniform ; but 
as it is she describes a variety of epicycles, in revolving 
monthly around the earth, and annually around the sun. 
These are represented in Fig. 3. 

Suppose the moon to be at A, and the earth in her 
orbit between A and 19, of course it would then be new 
moon. The earth and moon start on eastward in their 
respective orbits, or in the direction of the arrows. In 
about 14 days the moon will reach B, when she will be 
in opposition, and persons on the dark side of the earth, 
or during the night, will see her as a full moon. In 
about 14 days longer, she passes around to C, when it 
will again be new moon, &c. Thus throughout the year 
the figure. shows the earth's orbit and the moon's eccen- 
tric path, as well as the relative position of each, at 
each successive new and full moon. 

But it will be seen that the twelve revolutions of the 
moon, and the one revolution of the earth do not come out 
even ; or in other words, do not end at the same time. 
From the new moon at A, around to the new moon at D, 
are just twelve lunar months or revolutions; but at this 
time the earth wants 19° 20 7 to reach her starting point 
at A, or to complete her year. The lunar year, there- 
fore, consisting of twelve synodical revolutions of the 
moon, or 346 days, is 19 days shorter than the civil 
year. 



SIDEREAL AND SYNODIC REVOLUTION OF THE MOON. 79 



LESSON LXXIII. 

REVOLUTION OF THE MOON'S NODES AROUND THE ECLIPTIC. 

(Map 12.) 

By referring to Lessons XXX. and XXXI. it will be 
seen that the nodes of Mercury and Venus are per- 
manent ; that is that they are always at the same point 
in the ecliptic, or in the same longitude. But this is not 
the case with the Moon's nodes. Suppose the line pass- 
ing down from A, Fig. 3, to represent the line of her 
nodes, at the commencement of a lunar year. After 
twelve lunations, and when she has passed round to the 
point D, she will have returned to the satrfe node again, 
although she is 19° 20 7 short of the point where that 
node was reached 346 days before. At this time the 
line passing down from D would represent the line of 
her nodes. In this manner the nodes of the moon's 
orbit fall back westward, or recede 19-*-° every lunar 
year, till they complete a backward revolution quite 
around the ecliptic. To do this requires 18 years and 
225 days ; or 223 lunations ; when the moon will reach 
the same node again at D, or in the same longitude. 

This revolution of the moon's nodes will be noticed 
again in the chapter on Eclipses. The motion of the 
apsides will also be explained and illustrated in the chap- 
ter on Tides in connection with Map 14. 

LESSON LXXIV. 

STDEREAL AND SYNODIC REVOLUTION OF THE MOON. 

(Map 12.) 

The difference between a sidereal and synodic revo- 
lution of the planets is explained in Lesson LVII. A 
sidereal revolution of the Moon is a revolution from a 
particular star, around to the same star again ; or what 
would constitute a complete revolution if the earth were 
at rest. But as the earth is constantly advancing in her 
orbit, the moon, in passing from one full moon to another, 



80 ELEMENTARY ASTRONOMY. 

has to perform a Utile more than a complete revolution to 
bring her again in opposition to the sun. This extended 
journey is called her synodic revolution. 

The sidereal period is 27-J days, and the synodic 29-J-, 
as already stated, Lesson LXX. 



LESSON LXXV. 

REVOLUTION OF THE MOON UPON HER AXIS. 

(Map 12.) 

From the uniform appearance of the Moon's surface, 
even to the naked eye, it is obvious that she always pre- 
sents nearly the same side to the earth. From this fact 
it is concluded that she makes but one revolution upon 
her axis during her synodic revolution — that her motion 
upon her axis is from west to east — that her day (in- 
cluding a lunar day and night) must be equal to 29-J- of 
our days ; and that the earth is always invisible from 
one half of the moon's surface. 

By consulting Fig. 2, it will easily be seen that to 
keep the same side towards the earth, the moon must neces- 
sarily revolve once on her axis during her synodic revo- 
lution ; and also that if the side toward the earth at the 
full was towards us also at new moon, the side in dark- 
ness at full moon would be towards the sun, or enlight- 
ened at new moon. Observe, we are speaking of her 
actual light and shade, and not of her appearance from 
the earth. 

LESSON LXXVI. 

OF THE MOON'S LIBRATIONS. 

(Map 12.) 

Though the Moon always presents nearly the same 
hemisphere towards the earth, it is not always precisely 
the same. Owing to the ellipticity of her orbit, and the 
consequent inequality of her angular velocity, she ap- 
pears to roll a little on her axis, first one way and then 



TELESCOPIC VIEWS OF THE MOON* 81 

the other, thus alternately revealing and hiding new ter- 
ritory, as it were, on her eastern and western limbs. 
This rolling motion east and west is called her Miration 
in longitude. 

The inclination of her axis to the ecliptic gives her 
another similar apparent motion, alternately revealing 
and hiding her poles. This is called her libration in la- 
titude. Il may be illustrated by Map 4, Fig. 2, as ex- 
plained in Chapter VI. 



LESSON LXXVII. 

SEASONS OF THE MOON. 

The Moon's year consists of 29^ of our days ; and 
as she revolves but once on her axis in that time, it fol- 
lows that she has but one day and one night in her whole 
year. So slight is the deviation of her orbit from the 
plane of the ecliptic, and the inclination of her axis to 
the plane of her orbit, that the sun's declination upon 
her can never exceed 6° 40 7 . She must therefore have 
perpetual winter at her poles, while at her equator her 
long days are very warm, and her long nights very cold. 



LESSON LXXVIII. 

TELESCOPIC VIEWS OF THE MOON. 

(Map 12.) 
Fig. 4 is a telescopic view of the Moon, as she ap- 
pears when about a week old. The ragged line dividing 
her illuminated from her dark hemisphere, and extend- 
ing around the moon, is called the circle of illumination; 
and the portion of this circle towards the earth, as repre- 
sented on the map, is called the Terminator. This line 
traverses the moon's disc from west to east in about 15 
days, when it disappears from her eastern limb ; and the 
other half of the circle of illumination immediately ap- 

5* 



82 ELEMENTARY ASTRONOMY. 

pears on her western border. In about 15 days longer 
it passes around to the eastern limb again, as represented 
at Fig. 6, and at the change of the moon entirely disap- 
pears. 

The Figures 4, 5, and 6, are faithful representations 
of the moon, as she appears through a telescope of mo- 
derate power, at three different periods during a lunation. 



LESSON LXXIX. 

PHYSICAL CONSTITUTION OF THE MOON, MOUNTAINS, VOL- 
CANOES, ATMOSPHERE, ETC. 

(Map 12.) 

Nothing is more obvious, from a telescopic view of 
the Moon, than that her surface is remarkably rough and 
uneven. The evidence of this is, 

First, the crooked and ragged appearance of the ter- 
minator. Were the moon's surface level and smooth, 
this line would be uniform, and sharply defined. 

In the second place, small bright spots appear from 
time to4ime, from new to full moon, beyond the termina- 
tor, in the dark portions of the moon's disc. These are 
never far from the terminator, and grow larger and 
larger as it approaches them. In the same manner these 
bright spots linger after the terminator, from full to new 
moon, and grow smaller and smaller till they disappear. 

In the third place, after these spots fall fairly within 
the enlightened hemisphere of the moon, they project a 
shadow towards the terminator, or in a direction opposite 
to the sun. From new to full moon these shadows all 
point eastward, while from full to new moon again they 
all point westward. 

Now nothing can be more certain, from all these 
phenomena, than that the moon is covered with moun- 
tains. Being elevated above th£ common level of the 
moon's surface, the sun's light would fall upon their 
summits before the surrounding valleys were rendered 
luminous or visible by reflected light. As the light ad- 



GEOGRAPHY OF THE MOON, OR SELENOGRAPHY. 83 

vanced eastward it would enlarge the visible portions of 
the mountains ; and finally, after the space around them, 
west, north, and south, was enlightened, they would still 
cast shadows eastward. Besides, these shadows are al- 
ways darkest on the side towards the sun, or nearest the 
mountains. 

By examining Figures 4 and 6, in connection with 
the foregoing remarks, the student can hardly fail to be 
satisfied that the Moon also has her Alps, her Andes, and 
her Pyrenees. Some of her mountains have been esti- 
mated to be five miles in height. 

It has been ascertained also that many of the lunar 
mountains are of volcanic formation, like Etna and Ve- 
suvius. Dr. Herschel states that he actually saw the 
light of ihejires of several active volcanoes in the moon. 
The extravagant statement made by some authors, that 
cities, fortifications, and roads have been seen on the 
moon's disc, is worthy of little or no credit. It is much 
easier to imagine cities, &c. to exist on the moon's sur- 
face, than to actually see them even if they were there. 

In regard to the existence of an atmosphere around 
the moon, astronomers are divided. From observations 
during eclipses of the sun, and other phenomena, it is 
thought that if the moon has any atmosphere at all, it 
must be very limited in extent, and far less dense than 
that of the earth. 



LESSON LXXX. 

GEOGRAPHY OF THE MOON, OR SELENOGRAPHY. 

(Map 12.) 

The great natural divisions of the Moon's disc have 
received appropriate names. The following is a list of 
some of the principal mountains, the number answering 
to their locality as designated on the map, Fig. 5. It 
may require a near view to discover the figures and let- 
ters. 



84 ELEMENTARY ASTRONOMY. 

1. Tycho, 6. Eratosthenes, 

2. Kepler, 7. Plato, 

3. Copernicus, 8. Archimedes, 

4. Aristarchus, 9. Eudoxus, 

5. Helicon, 10. Aristotle. 

The dusky portions formerly supposed to be seas, are 
designated as follows : — 

A. Mare Humorum, E. Mare Tranquilitatis, 

B. " Nubium, F. " Serenitatis, 

C. " Imbrium, G. " Fecunditatis, 

D. " Nectaris, H. " Crisium.* 

The subject of Eclipses and Occultations will be con- 
sidered in Chapter IV. ; and that of Tides in Chapter V. 



LESSON LXXXI. 

MOONS OF JUPITER. 

(Map 2.) 

Jupiter has four satellites, whose distances, magni- 
tudes, and periodic times are as follows : — They are 
numbered in order, beginning with the one nearest to 
their primary. 

Distance. Periodic times. 

259,000 . . 1 day 18 hours. 

414,000 . . 3 " 12 « 

647,000 . . 7 " 14 " 

1,164,000 . . 17 " " 

By comparing the magnitude of Jupiter's satellites, 
with that of our moon, Lesson LXX., a striking resem- 
blance will be discovered. Indeed the size and distance 
of the first answer almost exactly to the size and distance 
of the Moon. But when we come to the periodic times, 
we find a vast disproportion. So great is the mass and 
attractive force of Jupiter, that if even his most distant 
satellite had a periodic revolution of twenty-nine and a 

* Olmsted's Introducton to Astronomy. 





Diameter in miles, 


1st 


2,500 . 


2d 


2,068 . 


3d 


3,377 . 


4th 


2,890 . 



SATELLITES OF SATURN. 85 

half days, its centripetal would overcome its centrifugal 
force, and it would fall to the body of the planet. To 
balance the great attractive force of the planet (Lesson 
XVII.) it is necessary that his secondaries should have a 
rapid projectile motion ; hence, though the first is as 
large, and as distant from Jupiter as our moon is from the 
earth, it revolves more ih&njifteen times as rapidly as the 
Moon. For remarks on the centripetal and centrifugal 
forces, see Lesson XX. 

The moons of Jupiter revolve nearly in the plane of 
his equator, and of course, nearly in the plane of his 
orbit and of the ecliptic. See XXXII. and XLIX. Their 
orbits, as stated by Dr. Herschel, are inclined to the plane 
of his equator, as follows : 

1st • . > 3° 5/ 30''. 

2d . . . . Variable. 

3d Variable. 

4th .... 2o 58/ 48". 
The eccentricities of the 1st and 2d are not per- 
ceptible. That of the 3d and 4th is small, and variable, 
in consequence of mutual perturbations, caused by their 
mutual attraction. They all revolve from west to east, 
or in the direction of the revolution of their primary upon 
his axis. 

The satellites of Jupiter may be seen with a teles- 
cope of very moderate magnifying power, or a common 
spy-glass ; and one of them has even been seen with the 
naked eye. This noble planet with his retinue of moons 
is the solar system in miniature ; and furnishes the most 
glorious confirmation of the truth of the Copernican 
theory. 

For eclipses of Jupiter's satellites see the chapter on 
eclipses. 

LESSON LXXXII. 

SATELLITES OF SATURN. 

(Map 2.) 
The satellites of Saturn are seven in number, and are 
seen only with telescopes of considerable power. They 



86 ELEMENTARY ASTRONOMY. 

revolve from west to east. The orbits of the six interior 
satellites are neary circular, and very nearly in the 
plane of the rings. That of the seventh is considerably 
inclined to the west, and approaches nearer to coincide 
with the ecliptic. 

Their distances and periodic times are as follows : 

Dist. in miles. Periodic times. 

1st 123,000 . . days 22 hours. 

2d 158,000 . . . 1 " 8 " 

3d 196,000 . 1 " 21 " 

4th 251,000 . . . 2 " 17 '« 

5th 351,000 . . 4 " 12 " 

6th 8 L 1,000 . . . 15 " 22 " 

7th 2,366,000 . 79 « 7 " 

Upon this subject an eminent astronomer remarks, 
that the satellites of Saturn have been much less studied 
than those of Jupiter. The most distant, is by far the 
largest, and is probably not much inferior to Mars in 
size. Its orbit is also materially inclined to the plane of 
the rings, with which those of all the rest nearly coin- 
cide. It is the only one of the number whose theory 
has been at all inquired into, further than suffices to 
verify Kepler's law of the periodic times, which holds 
good in this as in the system of Jupiter. It exhibits, 
like those of Jupiter, periodic defalcations of light, which 
prove its revolution on its axis in the time of a sidereal 
revolution about Saturn. 

The next in order, proceeding inwards, is tolerably 
conspicuous ; the three next very minute, and requiring 
pretty powerful telescopes to see them ; while the two 
interior satellites, which just skirt the edge of the rings, 
and move exactly in their plane, have never been dis- 
covered but with the most powerful telescopes which 
human art has yet constructed, and then only under 
peculiar circumstances. At the time of the disappear- 
ance of the ring (to ordinary telescopes) they have been 
seen* threading . like beads the almost infinitely thin 

' * By Sir William Herschel, in 1789, with a reflecting telescope 
of four feet in aperture. 



SUPPOSED SATELLITE OF LEVERRIER's PLANET. 87 

fibre of light, to which it is then reduced, and for a short 
time advancing off it at either end, speeding to return, 
and hasting to their habitual concealment.* 

LESSON LXXXIII. 

SATELLITES OF HERSCHEL. 

(Map 2.) 

Herschel has six satellites, as shown on the map, 
which revolve around him at the distances here laid down, 
and in the following periodic times : 





Dist.in miles. 


Periodic times. 


1st 


224,000 


5 days 21 hours, 


2d 


296,000 . 


8 " 17 " 


3d 


340,000 


10 " 23 " 


4th 


390,000 . 


. 13 " 11 " 


5th 


777,000 


38 " 2 " 


6th 


1,556,000 . 


. .117 " 17 " 



The satellites of Herschel are distinguished by two 
very remarkable peculiarities. By Lesson XXXII. it will 
be seen that his orbit very nearly coincides with the 
ecliptic. Now the orbits of his satellites, instead of being 
down near the plane of the ecliptic, as is the case with 
those of Jupiter, are elevated so as to cross it at an angle 
of near 80°. 

In the second place, while every other planet in the 
solar system, primaries as well as secondaries, revolve 
from west to east, the satellites of Herschel have a retro- 
grade or backward revolution. This singular anomaly is 
indicated on the map by the direction of the arrows. 

The orbits of Herschel's moons appear to be nearly 
circular. 

LESSON LXXXIV. 

SUPPOSED SATELLITE OF LEVERRIER's PLANET. 

From the observations of M. Lassell, as detailed on 
page 68, it is not improbable that this newly discovered 
* Herschel's Treatise. 



88 ELEMENTARY ASTRONOMY. 

world is attended by one or more secondary bodies. 
Indeed we might almost infer this from analogy, espe- 
cially when we consider the magnitude of the planet as 
answering pretty nearly to that of Herschel ; and his 
immense distance from the sun, upon which he also must 
depend for light and heat. This latter circumstance 
alone would seem to demand a profusion of moons to 
arrest the sunbeams in the surrounding space, and reflect 
them upon the cold and cheerless bosom of their pri- 
mary. For the present, however, the learner must con- 
tent himself with the little we are able to communicate 
upon this subject, in the hope that future observations 
may furnish us with a more satisfactory knowledge of 
the economy and peculiarities of this far distant orb. 

The secondary planets are all supposed to revolve on 
their respective axes, in the time of their periodic revolu- 
tions, so as always to present the same hemispheres to 
their respective primaries. No smaller bodies have ever 
been discovered revolving around the satellites, as moons 
or satellites to them. 



CHAPTER IV. 

OF ECLIPSES. 
LESSON LXXXV. 



NATURE AND CAUSES OF ECLIPSES. 

(Map 13.) 

An Eclipse is the partial or total obscuration or dark- 
ening of either the Sun or Moon. An eclipse of the Sun is 
called a Solar eclipse, and that of the Moon a Lunar 
eclipse* 

To understand the nature and philosophy of eclipses, 
it will be necessary to begin with what is called the law 
of shadows. The principles of this law are, as follows : — 



NATURE AND CAUSES OF ECLIPSES. 89 

1. A shadow is a portion of space deprived of light 
by the intervention of some dark or intransparent body*. 

2. The length and form of shadows depend not only 
on the form of the opaque body, by which the light is in- 
tercepted, but also upon its magnitude as compared with 
the luminous body ; and its distance from it. At Fig. 1 
the Sun is seen at S, on the right ; the Earth at B, and 
the Moon at A and C. The shadows of the Earth and 
Moon are seen projecting to the left, and running to a 
point. They have this form because the earth and moon 
are smaller than the Sun ; and as the earth is a globe, 
her shadow assumes the form of a cone, with its base 
towards the sun. 

3. If the earth were just as large as the sun, her shadow 
would be in the form of a cylinder ; and if larger than 
the sun it would spread out like a fan ; or like the sec- 
tion of a cone with its base turned from the sun. These 
principles may be illustrated at leisure by a candle and 
several balls of different sizes. 

4. When the opaque body is smaller than the lumi- 
nous one, the length of its conical shadow will depend 
upon its distance from the source of light. Thus, if the 
earth were at E, Fig. 1, her shadow would be shorter 
than represented in the figure by one half. 

5. The shadow cast by the earth is darker in some 
parts than in others. This is represented at O, and P P, 
Fig. 2. The deep conical shadow shown at O, and in 
all the other figures, is called the Umbra ; and the faint 
shadow shown at P P, the Penumbra. 

We are now prepared to state the causes of eclipses. 

6. An Eclipse of the Sun is caused by the moon, passing 
between the earth and the sun ; and casting her shadow 
upon the earth. This is represented at A, B, Fig. 1, 
where the moon is seen passing in her orbit around the 
earth, and hiding part of the sun's disc at S, from the 
observer at B ; or, what is the same thing, casting her 
shadow upon the earth at B. As the Moon is moving 
eastward, or in the direction of the arrows, she covers 
the low^er or western limb of the sun first, and advances 
to the east. By turning the right side of the map upper- 



90 ELEMENTARY ASTRONOMY. 

most for a moment, and placing it to the south of the 
learner, the figure can hardly fail to give him a correct 
and permanent idea. 

7. Eclipses of the Moon are caused by her falling into 
the earth's shadow, as represented at C. These com- 
mence on the moon's eastern limb, as may be shown by 
turning the left side of the map uppermost. 

8. In its natural position the map illustrates another 
fact : it shows why eclipses of the Sun always happen at 
new moon, and eclipses of the Moon at full moon. To 
an observer on the earth the moon must be new at A, and 

full atC. 

LESSON LXXXVI. 

EXTENT, DURATION, AND CHARACTER OF SOLAR ECLIPSES. 
(Map 13.) 

1. The first thing to be determined in regard to solar 
eclipses is the length of the moon's shadow. Let the 
reader now call to mind the fact that both the earth and 
moon move in elliptical orbits, as stated in Lessons XLIII. 
XLV. and LXX. Let him remember also, that the sun 
is in one of the foci of the earth's orbit, as represented in 
Fig. 2 ; and that the earth is in one of the foci of the moon's 
orbit, as shown at T and U. Now as the earth is farther 
from the sun at U, than at T, her shadow will be longer, 
and so with the moon. The shadows of both are much 
longer when the earth is at or near her aphelion as at U, 
than when near her perihelion as at T. 

2. The length of the moon's shadow is also modified 
by her position in her orbit. As her mean distance from 
the earth's centre is 240,000 miles, she must be 480,000 
miles nearer the sun at new moon than at her full. This 
difference in her distance must have its effect in length- 
ening or shortening her shadow. At T, Fig. 2, the earth 
is at hex perihelion, and her shadow and that of her sat- 
ellite are comparatively short. At U, the earth is at her 
most distant point from the sun ; and the shadows of 
both the earth and the moon are proportionably elongated. 



EXTENT, DURATION, ETC., OF SOLAR ECLIPSES. 91 

3. A third circumstance modifying the length of the 
moon's shadow, is the position of her aphelion and perihelion 
points, in respect to the sun. When the earth is at T, in 
her orbit, and the moon at her aphelion at M, which is 
then towards the sun, her shadow is the shortest possible ; 
as she is then nearer the sun than at any other time ; but 
when the earth is at her aphelion at U, and the moon 
comes to her aphelion when it is turned/rom the sun as 
at K, her shadow has its greatest possible length. Such 
is the variety of causes which conspire to affect the length 
of the shadows projected by the earth and moon. 

4. When the earth is at U, and the moon at her perihe- 
lion, and in conjunction as at H, her shadow will extend 
19,000 miles beyond the earth ; and will be nearly 175 
miles in diameter at the distance of the earth's surface. 
Consequently if her shadow fall centrally upon the earth, 
it will cover an area 175 miles in diameter, within 
which the sun will appear totally eclipsed. At this time 
the penumbra, will cover an area 5000 miles in diameter, 
within which the eclipse will be only partial. If the 
shadow falls upon the side of the earth, it will of course 
cover a much larger space ; and in either case, it will 
move from west to east over the earth's surface. 

5. When the earth is at T, and the moon at M, the 
shadow of the moon will not reach the earth by 20,000 
miles ; and when the sun and moon are at their mean 
distances from the earth, the cone of the moon's shadow 
will terminate a little before it reaches the earth's sur- 
face. 

6. The angular or apparent magnitude of a body de- 
pends much upon its distance from the observer (Les- 
son X.). When the sun and moon are at their mean 
distances, they appear nearly of a size ; but when the 
earth is at U, and the moon at H, the moon appears 
larger than the sun, and if a central eclipse take place, 
it will be total ; or, in other words, the moon will en- 
tirely cover or hide the sun's face. This is owing to the 
nearness of the moon to the earth, and the distance of 
the sun. A total eclipse may last 7 minutes and 58 
seconds. 



92 



ELEMENTARY ASTRONOMY. 



When the earth is at T, and the moon at M, the sun, 
being at his perihelion distance, will appear unusually 
large ; and the moon being in apogee, will appear unusu- 
ally small. Should a central eclipse happen at this time, 
the moon would not be large enough to hide the entire 
face of the sun, even when directly between us and him ; 
consequently in the middle of the eclipse the moon will 
be seen covering the centre of the sun, and leaving a 
luminous ring unobscured, as represented at V on the 
map. This is called an annular eclipse, and the ring 
may last 12 minutes and 24 seconds. 

7. For convenience in describing eclipses, the diameter 
of the sun and moon, respectively, is divided into twelve 
parts called digits. Thus at W, the sun would be des- 
cribed as about three digits eclipsed ; at S, about four 
digits, &c. 

The learner will now understand the difference be- 
tween partial and total, central and annular eclipses. 
Both annular and total eclipses must be central, but the 
annular eclipse is not total. The ring or outer border of 
the sun is left unobscured. 

" The following is a list of all the solar eclipses that 
will be visible in Europe and America during the re- 
mainder of the present century. To those which will 
be visible in New England the number of digits is an- 
nexed. 



Year. 


Month. 


Day and Hour. 


Digits. 


1847, 


Oct. 


9 1 A. M. 




1848, 


Mar. 


5 7 50 A. M. 


6i 


1851, 


July 


28 7 48 A. M. 


n 


1854, 


May 


26 4 26 P. M. 


Hi 


1858, 


Mar. 


15 6 14 A. M. 


if 


1859, 


July 


29 5 32 P. M. 


2i 


1860, 


July 


18 7 23 A. M. 


6i 


1861, 


Dec. 


31 7 30 A. M. 


H 


1863, 


May 


17 1 P. M. 




1865, 


Oct. 


19 9 10 A. M. 


H 



EXTENT, DURATION, ETC., OF SOLAR ECLIPSES. 



93 



Year. 


Month. 




Day and Hour. 


Digits. 


1866, 


Oct. 


8 


11 12 A. M. 





1867, 


Mar. 


6 


3 A. M. 




1868, 


Feb. 


23 


10 A. M. 




1869, 


Aug. 


7 


5 21 A. M. 


10 4 


1870, 


Dec. 


22 


6 A. M. 




1873, 


May 


26 


3 A. M. 




1874, 


Oct. 


10 


4 A. M. 




1875, 


Sept. 


29 


5 56 A. M. 


n| 


1876, 


Mar. 


25 


4 11 P. M. 


3^ 


1878, 


July 


29 


4 56 P. M. 


t\ 


1879, 


July 


19 


2 A. M. 




1880, 


Dec. 


31 


7 30 A. M. 


5i 


1882, 


May 


17 


1 A. M. 




1885, 


Mar. 


16 


35 A. M. 


H 


1886, 


Aug. 


29 


6 30 A. M. 


0\ 


1887, 


Aug. 


18 


10 P. M. 




1890, 


June 


17 


3 A. M. 




1891, 


June 


6 


Mer. 




1892, 


Oct. 


20 


19 P. M. 


si 


1895, 


Mar. 


26 


4 A. M. 




1896, 


Aug. 


9 


Mer. 




1897, 


July 


29 


9 8 A.M. 


4 1 


1899, 


June 


8 


Mer. 




1900, 


May 


28 


8 9 A. M. 


11 



The eclipses of 1854, 1869, 1875, and 1900, will 
be very large. In those of 1858, 1861, 1873, 1875, and 
1880, the Sun will rise eclipsed. 

Those of 1854, and 1875, will be annular. The 
scholar can continue this table, or extend it backwards, 
by adding or subtracting the Chaldean period of 18 years, 
11 days, 7 hours, 54 minutes, and 31 seconds.*" 



* Burritt. 



94 ELEMENTARY ASTRONOMY. 



LESSON LXXXVII. 

OF ECLIPSES OF THE MOON. 

(Map 13.) 

1. The average length of the earth's shadow is 860, 
000 miles ; or more than three times the moon's average 
distance from the earth. Its average breadth at the dis- 
tance of 240,000 miles from the earth's centre, or where 
the moon passes it, is about 6,000 miles ; or three times 
the moon's diameter. Now the extent and duration of a 
lunar eclipse must depend upon these three circumstan- 
ces : (1.) The distance of the earth from the sun, and 
the consequent length of her shadow at the time. (2.) 
The distance of the moon from the earth, which deter- 
mines the diameter of the earth's shadow where the moon 
passes it ; and (3.) The manner in which she passes 
through the earth's shadow. If it be greatly elongated, 
it will be proportion ably larger at the average distance 
of the moon's orbit; and if the moon is in perigee, and 
passes centrally through the earth's shadow, as at G and 
X, Fig. 2, the eclipse will be total, and long continued. 
On the other hand, if the moon is in apogee, she will pass 
the earth's shadow where it is comparatively slender as 
at K, and the eclipse will be of comparatively short dura- 
tion. So if she pass through the side of the shadow, in- 
stead of its centre, the eclipse will be partial instead of 
total. An eclipse of the moon can never be annular, as 
she cannot get so far off that the earth's shadow would 
be insufficient, when centrally passed, to cover the 
moon's disc. 

2. Before the moon enters the earth's shadow or um- 
bra, as at O, the earth begins to intercept from her por- 
tions of the sun's light, or to cast a faint shadow upon 
her. This shadow, called the moon's penumbra, grows 
darker and darker as she advances, till she enters the 
conical and perfect shadow of the earth. Here the real 
eclipse begins. The umbra and penumbra may be seen 
at O, and P P, on the map. 



OF THE TIME AND FREQUENCY OF ECLIPSES. 95 



LESSON LXXXV1II. 

OF THE TIME AND FREQUENCY OF ECLIPSES. 

(Map 13.) 

1. If the Moon's orbit lay in the plane of the eclip- 
tic, as represented at Fig. *1, there would be two central 
eclipses every month ; viz., one of the Sun and one of 
the Moon. But as the Moon's orbit is inclined to the 
ecliptic in an angle of 5o 9 y (Lesson LXX.), it is evident 
that she may be either above or below the ecliptic at the 
time of her conjunction with the Sun ; so that she will 
seem to pass either above or below him, and will not 
cause an eclipse. This will be understood by carefully 
observing the Moon's orbit at M and H, Fig. 2. At 
M, the side towards the Sun appears thrown up, or above 
the ecliptic ; while at H it is below the plane of the 
Earth's orbit. Of course, then, the Moon's shadow will 
pass below the Earth, as represented at H, and though it 
be ever so long there will be no eclipse. For the same 
reason, the Moon may pass either above or below the 
Earth's shadow, at the time of her opposition, and no 
lunar eclipse occur. 

2. It is only when the Moon is at or near one of her 
nodes, that either a solar or lunar eclipse can occur. 
On the Map, Fig. 2, the line L N represents the line of 
the nodes, as well as the plane of the ecliptic. The 
whole figure was intended to be in perspective. At A, 
the Moon is seen coming to her node, in the direction of 
the arrow, and casting her shadow upon the Earth. At 
the same time we see the eclipse advancing in the same 
direction, commencing upon the Sun's western limb at W. 
At-G and X, in the same figure, we see the Moon totally 
eclipsed. If, therefore, the Earth and the Moon reach 
the line of the Moon's nodes at the same time, the eclipse 
will be central, whether it be of the Sun or Moon. 

3. But it is not necessary that the Earth and Moon 
should be precisely on the line of the Moon's nodes, in 
order to produce an eclipse. " The distance of the 



96 ELEMENTARY ASTRONOMY. 

Moon from her node when she just touches the shadow 
of the Earth, in a lunar eclipse, is called the Lunar 
Ecliptic Limit ; and her distance from the node in a solar 
eclipse, when the Moon just touches the solar disc, is 
called the Solar Ecliptic Limit. The Limits are re- 
spectively the farthest possible distances from the node 
at which eclipses can take place."* 

The Lunar Ecliptic Limit is 11° 25' 40''. This is the 
greatest distance from the Moon's node at which a lunar 
eclipse can take place ; and in the event of its happening 
at such a distance from the node, it must be exceedingly 
small or slight. 

The Solar Ecliptic Limit is 16° 59'. If at the mo- 
ment of new moon her node be more than this distance 
from the Sun, no eclipse can happen. 

This subject may be elucidated by contemplating the 
Moon as seen in her orbit at A, Fig. 2. As she ap- 
proaches her node, it is evident that she will overlap or 
eclipse the Sun, as soon as she gets as near the ecliptic 
as the Sun's semi-diameter; as just one-half the Sun is 
above the ecliptic. That point, therefore, in the Moon's 
orbit which is only the semi-diameter of both the Sun and 
Moon from the ecliptic, is the ecliptic limit for solar 
eclipses. 

4. The Moon's nodes constantly fall back westward 
on the ecliptic, at the rate of about 19° per year; so 
that she comes to the same node again, as from the line 
near A, Fig. 2, around to A again, in 19 days less than 
a year ; or in 346 days, hi just half this time, viz., 
173 days she passes her other node in the opposite side 
of the ecliptic, as at N. It follows, therefore, that at 
whatever time of year we have eclipses at either node, 
we may be sure that in 173 days afterwards we shall 
have eclipses at the other node. And as for any given 
year eclipses commonly happen in two opposite months, 
as January and July, February and August, May and 
November, these opposite months, whichever they may 
be, are called for that year the Node Months. 

* Olmsted. 



ECLIPSES, OR OCCULTATIONS OF THE STARS. 97 

5. There cannot be less than two nor more than 
seven eclipses in one year. If but two, they will both 
be of the Sun ; but if seven, five will be of the Sun and 
two of the Moon. The usual number is two solar and 
two lunar. 



LESSON LXXXIX. 

ECLIPSES, OR OCCULTATIONS OF THE STARS. 

An occultation of the stars is caused by the Moon 
passing between us and them, and concealing them from 
our view. Though a very simple and common phenome- 
non, it is, nevertheless, a very interesting one. At New 
Moon, especially, the star occulted may be traced to the 
very border of the Moon's eastern limb, when it sud- 
denly goes out. From these stellar occultations, or 
eclipses of the stars, many important conclusions may 
be drawn. They teach us that the Moon is an opaque 
body, terminated by a real and sharply defined surface, 
intercepting light like a solid. They prove to us, also, 
that at those times when we cannot see the Moon, she 
really exists, and pursues her course \ and that when we 
see her only as a crescent, however narrow, the whole 
globular body is there, filling up the deficient outline, 
though unseen. For occultations take place indiffer- 
ently at the dark and bright, the visible and invisible 
outline, whichever happens to be towards the direction 
in which the Moon is moving ; with this only difference, 
that a star occulted by the bright limb, if the phenomenon 
be watched with a telescope, gives notice, by its gradual 
approach to the visible edge, when to expect its disap- 
pearance ; while, if occulted at the dark limb, if the 
?vloon, at least, be more than a few days old, it is, as it 
were, extinguished in mid-air, without notice or visible 
cause for its disappearance, which, as it happens instan- 
taneously, and without the slightest previous diminution 
of its light, is always surprising ; and, if the star be a 
large and bright one. even startling from its suddenness. 

6 



98 ELEMENTARY ASTRONOMY. 

The re-appearance of a star, too, when the Moon has 
passed over it, takes place, in those cases when the 
bright side of the Moon is foremost, not at the concave 
outline of the crescent, but at the invisible outline of the 
complete circle, and is scarcely less surprising from its 
suddenness, than its disappearance in the other case.* 

LESSON XC. 

eclipses of jupiter's moons. 

Every planet in the Solar System, whether primary 
or secondary, casts its shadow in the direction opposite to 
the Sun. But none of the primaries can eclipse each other. 
In every case, however, where they are attended by sa- 
tellites there may be eclipses. 

Of the number, distances, magnitudes, and motions 
of Jupiter's moons, we have already spoken in Lesson 
LXXXI. It remains now to consider their eclipses. From 
the magnitude of Jupiter, and his distance from the Sun, 
it will be seen at once that he must cast a shadow of 
great dimensions, extending far into space towards the 
orbit of Saturn. But in order fully to understand the 
subject of his eclipses, it will be necessary to take into 
the account not only his distance, magnitude, &c, but 
the near coincidence of his orbit with the ecliptic, his 
equator with his orbit, and the orbits of his moons with 
his equator. All these points will be found duly noticed 
under their appropriate heads in the preceding lessons. 
Let it be remembered then — 

1. That Jupiter casts a broad and long shadow in the 
direction opposite the Sun. 

2. That the centre of this shadow lies in the plane of 
his orbit, which differs only \\° from the plane of the 
ecliptic. (XXXII.) 

3. That his axis is inclined to his orbit only 3° 5 y , 
and of course the plane of his equator nearly coincides 
with that of his orbit. (XLIX.) 

* HerschePs Astronomy. 



ECLIPSES OF SATURN -AND HERSCHEL. 99 

4. Three of his moons revolve very nearly in the 
plane of his equator, and must consequently pass near 
the centre of his shadow at every revolution. They 
must, therefore, be totally eclipsed. 

5. The most distant of his satellites has an orbit more 
inclined to the ecliptic, so that she sometimes but just 
grazes the border of the shadow in passing, and some- 
times wholly escapes. But these instances are compara- 
tively rare. As a general rule, it may be said that the 
satellites of Jupiter are totally eclipsed at every revolution ; 
so that by determining the number of revolutions each 
makes in a month (Lesson LXXXI.), and adding them 
together, we find the number of eclipses in that period 
of time. They amount to about forty. 

6. From the nearness of his satellites (LXXXI.) we 
infer that they must pass his shadow where its diameter 
must be nearly as great as that of Jupiter ; hence the 
eclipses last for some time. 

7. The shadows of the satellites, being much longer 
than those of our Moon, on account of their greater dis- 
tance from the Sun, and some of them being much nearer 
Jupiter than our Moon is to the Earth, cast their shadows 
upon him at every revolution. They may be seen with 
good telescopes " like small round ink spots" traversing 
his disc. 

8. The entrance of Jupiter's moons into his shadow is 
called their immersion ; and their egress therefrom their 
emersion. Tables have been constructed showing the pre- 
cise time when these shall take place, for a given longitude 
on the Earth, as for instance Greenwich Observato- 
ry, which tables are employed, in connection with a 
chronometer or accurate time-piece, for determining ter- 
restrial longitude. 

LESSON XCI. 

ECLIPSES OF SATURN AND HERSCHEL. 

Of the satellites of these two planets, too little is 
known to admit of any very positive statements in re- 



100 ELEMENTARY ASTRONOMY. 

spect to their eclipses. Indeed very little is said upon 
this subject, even by the ablest practical astronomers. 
Of Saturn it is remarked by Dr. Herschel, that owing to 
the obliquity of his rings, and of the orbits of his satel- 
lites to the ecliptic, they suffer no eclipses, the interior 
ones excepted, until near the time when the rings are seen 
edgewise. (See Lesson LXVI. and Map.) 

Of the eclipses of HerschePs moons, nothing whatever 
is known by observation, and very little by theory, as 
deduced from their distances, inclination of orbits, &c. 



CHAPTER V. 

PHILOSOPHY OF THE TIDES. 
LESSON XCII. 

OF THE NATURE AND CAUSES OF TIDES. 

(Map 14.) 

The alternate rising and falling of the waters of the 
ocean are called Tides. The rising of the waters is 
called Flood tide, and their falling Ebbtide. There are 
two flood and two ebb tides every day. 

The cause of the tides is the attraction of the Sun 
and Moon upon the Earth and the waters surrounding it. 

Fig. 1 represents the Earth surrounded by water in 
a state of rest, or as it would be were it not acted upon 
by the Sun and Moon. 

Fig. 2 shows the Moon at a distance above the Earth, 
and attracting the waters of the ocean so as to produce a 
high tide at B. But as the Moon makes her apparent 
westward revolution around the Earth but once a clay, 
the simple raising of a flood tide on the side of the Earth 
towards the Moon, would give us but one flood and one 
ebb tide in 24 hours ; whereas it is known that we have 
two of each. 



OF THE NATURE AND CAUSES OF TIDES. 101 

Fig. 3, therefore, is a more correct representation of 
the tide-wave, as it actually exists, except that its height, 
as compared with the magnitude of the Earth, is vastly 
too great. It is designed merely to illustrate the princi- 
ple under consideration. While the Moon at A pro- 
duces a high tide at B, we see a high tide at C, on the op- 
posite side of the Earth. Of course, it is low tide, at this 
time, at D and E ; and as these four tides traverse the 
globe, from east to west every day, it accounts for the 
rising and falling of the tides every twelve hours. 

But the most difficult point remains yet to be elucidated. 
" The tides,'' says Dr. Herschel, " are a subject on 
which many persons find a strange difficulty of concep- 
tion. That the Moon, by her attraction, should heap up 
the waters of the ocean under her, seems to most persons 
very natural — that the same cause should, at the same 
time, heap them up on the opposite side of the Earth, [as 
at C, Fig. 3,] seems to many palpably absurd. Yet no- 
thing is more true, nor indeed more evident, when we 
consider that it is not by her ichole attraction, but by the 
differences of her attractions at the two surfaces and at 
the centre, that the waters are raised.' 7 * 

The law of gravitation (XVII.) is the same which 
prevails in the diffusion of light (XII.), namely, that its 
force is, inversely, as the squares of the distances ; or, in 
other words, as the square of the distance is diminished, 
the force of attraction is increased, and vice versa. Let 
this rule be applied to the Earth and Moon, Fig. 3. 

1. In the first place, nothing can be more evident 
than that the tide water at B is the whole diameter of 
the Earth, or 8000 miles nearer the Moon at A than the 
waters of the opposite side of the Earth at C. They 
must also be 4000 miles nearer than the centre of the 
earth, or the parts between D and E ; while these parts, 
in turn, are 4000 miles nearer than the waters at C. 

2. Now as the force of the Moon's attraction depends 
upon her distance, it must follow, in the second place, 
that the different parts of the Earth will be unequally at- 

* Treatise, 315. 



102 ELEMENTARY ASTRONOMY. 

traded. B will be attracted more than D E, and D E 
more than C. 

3. This unequal attraction of the different parts of the 
Earth's surface will tend to separate these parts. As B is 
more strongly attracted than the body of the Earth, it will 
be drawn farther towards the Moon, so as to produce a high 
tide on that side of the Earth. The body, or solid parts 
of the Earth, being nearer to the Moon than the waters 
at C, will also recede from them towards the Moon, caus- 
ing the waters to tend from D E towards C, and raising 
a high tide at that point. 

4. This perturbation or swinging of the Earth one 
way and the other, in her orbit, is a constant result of 
the Moon's attraction. Though the Earth never deviates 
from her course more than the amount of her diameter, 
yet this is considered sufficient to account for the high 
tides opposite the Moon, when in conjunction with the 
Sun, upon the principles already explained. 



LESSON XC1II. 

LAGGING OF THE TIDE EXCURSIONS IN LATITUDE. 

(Map 14.) 

1. The vertex, or highest point of the tide- wave, is 
generally about three hours behind the Moon in her pas- 
sage westward. This is illustrated at Fig. 4, where the 
Moon is seen on the meridian at A, and the tide-wave 
hanging back to the east, with its vertex at B. The 
tide will be rising at C when the Moon passes the meridian ; 
and will continue to rise for three hours afterwards 
when it will begin to ebb again. 

The cause of this delay of the tide-wave is a want of 
time for it to yield to the impulse given to the waters by 
the Moon's attraction. Besides, the Moon continues to 
act upon the waters east of her meridian, for some time 
after she has passed over them. 

2. Not only does the tide lag behind the Moon, but 
the Moon lags behind her hour, so to speak, or rises 



SPRING AND NEAP TIDES. < 103 

later and later every night, as she advances eastward in 
her orbit ; so that high or low water is about fifty minutes 
later every day, in reaching any particular meridian, 
than on the day preceding. 

3. The position of the Moon in regard to the equi- 
noctial has also its effect in modifying the tides. This 
is illustrated at Fig. 5, where the Moon is seen at A, south 
of the equinoctial, and the vertex of the tide-wave at B, on 
the Tropic of Capricorn. Of course the vertex of the op- 
posite wave would be at E, in the northern hemisphere. 
Were the Moon at C, or north of the equator, the vertices 
of the wave would be shifted from B and E to D and F. 
It is in this way that the declination of the Sun and 
Moon (XL VII.) materially affects the tides in any parti- 
cular latitude. As the vertex of the tide-wave tends to 
place itself vertically under the luminary which produces 
it, when this vertical changes its point of incidence on 
the surface, the tide- wave must tend to shift accordingly ; 
and thus, by monthly and annual periods, must tend to 
increase and diminish alternately the principal tides. 
The period of the Moon's nodes is thus introduced into 
this subject ; her excursions in declination in one part of 
that period being 29°, and in another only 17°, on either 
side of the equator.* 

It is on this account, that in high latitudes every al- 
ternate tide is higher than the intermediate ones, the 
evening tides in summer exceeding the morning tides, 
and the morning tides in winter exceeding those of the 
evening. 

WESSON XCIV. 

SPRING AND NEAP TIDES. 

(Map 14.) 

1. We have hitherto spoken chiefly of the Moon as 
instrumental in the production of the tides ; but though 
she is the principal, she is not the only cause. The mass 
of the Sun is seventy millions of times greater than that 

* Herschel's Treatise, 317, 318. 



104 ELEMENTARY ASTRONOMY. 

of the Moon (LXX.), but in consequence of his great 
distance, his attractive force upon the Earth is only about 
one-third as great as that of the Moon. Still it is amply 
sufficient to produce a perceptible tide-wave of itself, in- 
dependently of the aid of the Moon. Now as the solar 
and lunar attractions are to each other as one to three, it 
is evident that when the two forces are combined they 
will produce tides one-third greater than usual ; and when 
they counteract each other, the lunar tide- wave will 
prevail, but will be one-third lower than usual. These 
extraordinary variations are called the Spring and Neap 
tides. There are two of each every month; the spring, 
or highest tides, occurring at the syzygies, or at New 
and Full Moon, and the neap tides at her quadra- 
tures. 

A, B, C, F, Fig. 6, are intended to illustrate these 
phenomena. At A, the Moon is seen in conjunction, as 
it is New Moon, so that they act together upon the 
waters of the ocean, and produce a Spring tide. The map 
shows the tide-wave as considerably higher than at F 
or B. 

2. At B, the Moon has passed to her first quarter, so 
that Ijer attraction is in a direction at right angles with 
that or the Sun. But as she exerts three -fourths of all the 
attractive force of the Sun and Moon both, she succeeds 
in producing a lunar tide in spite of the Sun, though he 
subtracts one-third from what would otherwise be its 
elevation. On these principles we account for the Neap 
tides. 

3. At C, the Sun and Moon are seen in opposition, 
when the Earth exhibits another spring tide. But here 
the tide- wave opposite to each luminary respectively, 
cannot be materially augmented by the perturbations of 
the body of the Earth, as illustrated at Fig. 3, and ex- 
plained at the beginning of this chapter ; for as the Sun 
and Moon act in direct opposition to each other, they 
tend to keep the Earth from swinging towards either. 
But as the Moon has three times the force of the Sun, she 
will attract the Earth towards her, in spite of the Sun, so 
that she will thus contribute to the production of the 



SPRING AND NEAP TIDES. ' 105 

tide-wave on the side of the Earth towards C. On the 
hemisphere towards the Moon, she must raise her own 
tide, and that, too, with the whole force of the Sun's at- 
traction acting against her. How, then, can there be a 
spring tide at this time on the side opposite the Sun ? 
And yet such is the fact. 

Here is a point which it must be acknowledged is not 
satisfactorily explained by the prevailing theory of the 
philosophy of tides. When the Sun and Moon are in 
opposition, they must necessarily diminish that perturba- 
tion of the Earth, which is assumed to be the cause of 
spring tides, and as the cause is reduced the effect also 
should be reduced. According to this theory, therefore, 
we ought to have a neap instead of a spring tide, when the 
Sun and Moon are in opposition. The Earth cannot swing 
in two opposite directions at the same time. Even Prof. 
Olmsted, whose abilities as an astronomer and mathemati- 
cian are universally acknowledged, seems to be at a loss 
here. He says: — "At the time of New Moon, the Sun and 
Moon both being on the same side of the Earth [as repre- 
sented at A and D], and acting upon it in the same line, 
their actions conspire, and the Sun may be considered as 
adding so much to the force of the Moon. We have 
already explained how the Moon contributes to raise a 
tide on the opposite side of the Earth. But the Sun, as 
well as the Moon, raises its own tide- wave, which, at 
New Moon, coincides with the lunar wave. At Full 
Moon, also, the two luminaries conspire in the same way 
to raise the tide ; for we must recollect, that each body 
contributes to raise the tide on the opposite side of the 
Earth, as well as on the side nearest to it. At both the 
conjunctions and oppositions, therefore, that is, at the 
syzygies, we have unusually high tides. 5 '* 

Here, it will be seen, that the learned author speaks 
of the fact of spring tide at Full Moon, and refers to the 
general principles upon which we account for spring 
tide at New Moon ; but how the Sun and Moon, acting 
in opposition, can produce spring tides, remains to be 
explained. 

* Introduction to Astronomy, 168. 
6* 



106 ELEMENTARY ASTRONOMY. 

4. At F, we see the Moon in the neighborhood of lief 
last quarter, and the Earth exhibiting the neap tides 
again. We have thus passed through with one lunation, 
in which we have at A and C, two spring tides, and at 
B and F two neap tides. 

5. The spring tides are not at their height at the 
moment of the syzygies, but about thirty-six hours after- 
wards. 

PROFESSOR DAVIES 5 THEORY. 

Since the foregoing was in type, the author accident- 
ally met with Prof. Davies ? formerly of West Point, who 
in view of the exceptions we had taken to the prevailing 
philosophy, on the preceding page, submitted the follow- 
ing theory. So far as we can discover, it is a philoso- 
phical one, and it is certainly more satisfactory upon 
some points than the prevailing doctrine, which we had 
previously ventured to call in question. In the correct- 
ness of his theory, Prof. D. expresses entire confidence; 
and by his consent it is here inserted for the benefit of 
the reader. 

The principle upon which he accounts for the tides, 
is that of hydrostatic pressure. When fluids of different 
specific gravity are mingled together, the heavier will 
displace the lighter, and cause it to rise to the surface. 
If the waters of the ocean were not acted upon by the 
Sun or Moon, their specific gravity would be the same 
all over the world ; and they would consequently balance 
each other, producing equilibrium, as represented at 
Fig. 1. But they do attract the waters of the ocean, 
and destroy their equilibrium. Take the Earth and 
Moon as represented at Fig. 3. While the Moon is at 
A, the tendency of her attraction is to diminish the 
specific gravity or weight of the waters at B, as she over- 
comes a portion of the Earth's gravitating force ; so that 
these waters become lighter than they are wont to be. 
At the same time the Moon acts upon the waters at D E 
with a slightly diminished force ; but the tendency at 
these points is in a horizontal direction, or from D E to- 
wards A, and not away from the Earth's centre. Of 
course, then, the specific gravity of the water is not 



OTHER INEQUALITIES OF THE TIDES. 107 

lessened at D and E. But as the waters at B are rendered 
lighter by the Moon's attraction, the waters at D E, hav- 
ing retained their usual weight, will displace the former, 
thus causing the waters to rise at B and C. In a word, 
the difference in the direction of the Moon's attraction at 
B and D E, as respects a perpendicular to the Earth's 
centre, makes a difference in the iveight of the waters at 
these two points ; and the waters at D E, being heaviest, 
sink down till the lighter waters at B and C are enough 
higher to balance them ; or till equilibrium is produced. 
This theory applies as well to spring tides at Full 
Moon as to any other tides ; and besides, it requires no 
sensible perturbations of the Earth as the result of the 
Moon's attraction. It may, however, be liable to this ob- 
jection : that when the Sun and Moon are in opposition, 
they will counteract each other's influence in reducing 
the specific gravity of the waters on the side of the 
Earth opposite them respectively, and thus prevent rather 
than cause a spring tide. 

LESSON XCV. 

OTHER INEQUALITIES OF THE TIDES. 

(Map 14.) 

1. The tides vary in height, according to the dis- 
tances of the Earth and Moon at the time when they 
occur. Take, for example, the spring tides at New 
Moon. If the Earth is at her aphelion distance from the 
Sun, and the Moon in apogee, as we see represented at A, 
Fig. 6, the attraction of both the Sun and Moon will be 
less than their average amount, so that there will be but 
a moderate spring tide ; but if the Moon is in perigee, 
and the Earth at her perihelion, as seen at D, both the 
Sun and Moon, being at their nearest points to the Earth, 
and in conjunction, will exert their full attractive influ- 
ence upon the Earth ; and the spring tide will be unu- 
sually high, as shown on the map. 

2. At E the earth is near her perihelion, and the 
Moon in opposition and in apogee. In such a case the 
Sun has his greatest agency in producing the tides and 



108 ELEMENTARY ASTRONOMY. 

the Moon her least. This will tend to equalize their 
forces. 

3. The height of the tides in different parts of the 
world is exceedingly various, owing to their being crowded 
into narrow channels in some instances, and to various 
other local causes. In open seas the spring tides are 
about eleven, and the neap tides about seven feet. At 
London the spring tides rise to the height of nineteen 
feet ; at the mouth of the Indus thirty feet ; in the river 
Severn, England, forty feet ; at St. Maloes, in France, 
forty-five feet; and at Cumberland, Bay of Fundy, seven- 
ty-one feet. This last is the highest tide in the world, 
and is caused by the meeting of the great northern and 
southern tide-waves of the Atlantic, which here come 
together in opposite directions. 

The height of tides on different portions of the western 
continent has been given as follows : 

Cumberland, Bay of Fundy, . . . 71 feet. 

Boston, . . . . 11 " 

New Haven, . . . . 8 " 

New- York, 5 " 

Charleston, S. C 6 " 

This table seems to accord well with the theory just 
named, in regard to the cause of the excessively high 
tides in the Bay of Fundy. 

4. The lagging of the tide-wave behind the Moon 
(Lesson XCIII.) is greatly modified by local causes. 
Though the tides are usually highest about three hours af- 
ter the Moon has passed the meridian, it is often retarded 
by shoals and channels, and by striking against capes and 
headlands, so that, as exceptions to the general rule, high 
tides happen at all distances of the Moon from the meri- 
dian. 

5. Lakes and inland seas have no tides, in conse- 
quence of their inconsiderable magnitude, as compared 
with the waters of the ocean. 

6. Dr. Herschel observes that the action of the Sun 
and Moon produces tides in the atmosphere, as well as in 
the water ; and that delicate observations have rendered 



MOTION OF THE APSIDES OF THE MOON's ORBIT. 109 

them sensible and measurable. The pupil will find a 
remark concerning tides on the Sun, in Chapter VII. , 
where the various theories of the solar spots are consid- 
ered. 

LESSON XCVI. 



MOTION OF THE APSIDES OF THE MOON S ORBLT. 
(Map 14.) 

At the close of Lesson LXXIII. we promised in this 
chapter to speak of the motion or revolution of the Moon's 
apsides. The apsides of the Moon's orbit are her peri- 
helion and aphelion points; and the line of the apsides is 
a line drawn through those points, as shown in Fig. 6, 
wherever the Moon's orbit is represented. At A this 
line is marked M A. 

Now the motion of the apsides is the revolution of 
these points around the ecliptic from west to east. The 
map shows this revolution as we trace the Moon around 
from A to F, in which place the line of the apsides, or 
the major axis of the ellipse, is at right angles with itself, 
as shown at A. 

The apsides of the Moon's orbit make a complete 
revolution in about nine years. In four and a half years 
the line A M will shift ends, so that the perihelion point 
M will be towards the Sun ; and in four and a half years 
more it will shift ends again, so that the Moon will reach 
her perigee again at M, or in the same part of the heavens. 
In this way the apsides constantly advance eastward, 
till, at the end of nine years, they finish a complete revo- 
lution. 

It must not be supposed from what we have said 
above, that the apsides shift ends suddenly, or all at 
once. This is not the case. Their motion is gradual 
and uniform, as shown on the map. 

As already stated in the chapter on that subject, the 
motion of the Moon's apsides must always be taken into 
the account in calculating Eclipses, as well as in the 
explanation of the Tides. 



110 ELEMENTARY ASTRONOMY. 

CHAPTER VI. 

OF COMETS. 
LESSON XCVII. 

GENERAL DESCRIPTION OF COMETARY BODIES. 
(Map 15.) 

1 . Comets are the most singular class of bodies belong- 
ing to the Solar System. They derive their name from 
the Greek word coma, which signifies bearded or hairy. 

2. A comet usually consists of three parts — the Nu- 
cleus, the Envelop, and the Tail. The Nucleus is what 
may be called the body or head of the comet, as seen at 
N, on the map. The Envelop is the nebulous or hairy 
covering that surrounds the nucleus. It may be seen 
around the nuclei of several of the specimens on the 
map, and especially that of 1585. The Tail of a comet 
is an expansion or elongation of the envelop. 

3. Some comets have no perceptible nucleus, their 
entire structure being like that of a thin vapory cloud, 
passing rapidly through the heavens. 

4. Many comets have simply the envelop, without 
any tail or elongation. Such were those that appeared 
in 1585 and 1763, the former of which will be found on 
the map. 

5. Cassini describes the comet of 1682 as being as 
round and as bright as Jupiter, without even an envelop. 
But these are very rare exceptions to the general charac- 
ter of cometary bodies. 

6. The tails of comets usually lie in a direction op- 
posite to the Sun ; so that from perihelion to aphelion they 
precede their nuclei or heads ; or in other words, comets 
seem, after having passed their perihelion, to back out of 
the Solar System. See Map 2. 

7. The comet of 1823 is said to have had two tails, 
one of which extended towards the Sun. This comet 
may be seen on the map, with a portion of its orbit. 
The Sun is supposed to be on the left, and the comet pass- 



GENERAL DESCRIPTION OF COMETARY BODIES. Ill 

ing down towards its perihelion. Its nucleus and envelop 
are distinctly represented. 

8. The tails of comets are usually curved more or 
less, being concave towards the region from whence they 
come. This is well shown in the comets of 1823, 1811, 
and 1680. That of 1689 is said to have been curved 
like a Turkish sabre, as shown on the map. 

The cause of this curvature of the tails of comets is 
supposed to be a very rare ethereal substance, which 
pervades space, and offers a slight resistance to their 
progress. Of course it must be almost infinitely atten- 
uated, as the tails themselves are a mere vapor, which 
could make no progress through the spaces of the heavens 
were they not very nearly a vacuum. They could no 
more pass a medium as dense as our atmosphere, than 
an ordinary cloud could pass through the waters of the 
sea. 

9. Comets have been known to exhibit several tails at 
the same time. That of 1744, represented on the map, 
had no less than six tails spread out in the heavens like 
an enormous fan. 

10. The tails of comets do not continue of the same 
uniform length. They increase both in length and 
breadth as they approach the Sun, and contract as they 
recede from him, until they often nearly disappear before 
the comet gets out of sight. 

11. Instances have occurred in which tails of comets 
have been suddenly expanded or elongated to a great 
distance. This is said to have been the case with the 
great comet of 1811. 

12. Of the physical nature of comets little is known. 
That they are in general very light and vapory bodies is 
evident from the fact that stars have sometimes been seen 
even through their densest portions, and are generally 
visible through their tails ; and from the little attractive 
influence they exert upon the planets in causing pertur- 
bations. While Jupiter and Saturn often retard and 
delay comets for months in their periodic revolutions, 
comets have not power in turn to hasten the time of the 
planets for a single hour ; showing conclusively that the 



112 ELEMENTARY ASTRONOMY. 

relative masses of the comets and planets are almost 
infinitely disproportionate. The comet of 1770 got 
entangled by attraction, among the moons of Jupiter, on 
its way to the Sun, and remained near them for four 
months ; yet it did not sensibly affect Jupiter or his 
moons. In this way the orbits of comets are often en- 
tirely changed. That they are in themselves opaque 
bodies, and shine only by reflected light, is evident from 
their sometimes exhibiting distinct phases — from their 
increased brightness as they approach the Sun, and from 
the known difference in the properties of direct and 
reflected light. 



LESSOxN XCVIII. 

MAGNITUDES, VELOCITIES, TEMPERATURE, PERIODS, DIS- 
TANCES, NUMBERS, ETC. OF COMETS. 

(Map 15.) 

1. The heads or nuclei of comets are comparatively 
small. The following table shows the estimated diame- 
ter in five different instances. 

The comet of 1778, diameter of head 33 miles. 

" 1805, " 36 " 

" 1799, " 462 " 

1807, " 666 " 

" 1811, " 428 " 

2. The tails of comets are often of enormous length 
and magnitude. That of 371 before Christ was 60° long, 
covering one third of the visible heavens. In 1618, a 
comet appeared which was 104° in length. Its tail had 
not all risen when its head reached the middle of the 
heavens. That of 1680 (see map) had a tail 70° long, 
so that though its head set soon after sundown, its tail 
continued visible all night. 

The following table will show the length of the tails 
of some of the most remarkable comets, both in degrees 
and in miles. They will be identified only by the year 
when they appeared. 



MAGNITUDES, VELOCITIES, ETC., OF COMETS. 113 

B. C. 371, 60° . . 140,000,000 miles. 

A. D. 1456, 60 . . 70,000,000 " 

" 1618, 104 . . 65,000,000 " 

" 1680, .70 . . 123,000,000 " 

" 168), 68 . . 100,000,000 " 

" 1744, 30 . . 35,000,000 " 

" 1769, 90 . . 48,000,000 " 

" 1811, 23 . . 132,000,000 " 

11 1843, 60 . . 130,000,000 " 

As these estimates are the angles under which they 
were viewed from the earth, the length of their tails in 
miles would not be proportional to the angle merely, as 
their distances must also be taken into the account. So 
the comet of 1843, with an angular length of only 60° was 
longer in fact by 65,000,000 miles than the comet of 
1618, with an angular length of 104°. At the time of 
measurement the latter was much nearer to the earth 
than the former when his dimensions were estimated. 

The learner should look up the comets named in the 
above table, so far as laid down on the map. 

3, The velocity with which comets often move, is 
truly wonderful. Their motions are accelerated as they 
approach, and retarded as they recede from the Sun ; so 
that their velocity is greatest while passing their peri- 
helions. The comet of 1472 described an arc of the 
heavens of 120° in extent in a single day ! That of 
1680 moved, when near its perihelion, 1,000,000 miles 
per hour. 

4. The temperature of comets when nearest to the 
Sun must be very great. That of 1680 came within 
130,000 miles of the Sun's surface, and must have re- 
ceived 28,000 times the light and heat which the Earth 
receives from the Sun — a heat more than 2,000 times 
greater than that of red-hot iron. What substance can 
a comet be composed of to endure the extremes of heat and 
cold to e which it is subject ? Some have supposed that 
their tails were caused by the Sun's light and heat rare- 
fying and driving back the vapory substance composing 
the envelop. 



114 ELEMENTARY ASTRONOMY. 

5. The periods of but few comets are known. 
That of 1818, called " Encke's Comet" has a period of 
only 3-J- years. Biela's Comet has a period of 6 \ years. 
That of 1682 (then first noticed with care, and identi- 
fied as the same that had appeared in 1456, 1531 and 
1607) has a period of about 76 years. It is called 
Halleifs Comet, after Dr. Halley, who determined its 
periodic time. 

The great comet of 1680 has a periodic time of 570 
years, so that its next return to our system will be in the 
year 2,250. Many are supposed to have periods of thou- 
sands of years, and some have their orbits so modified 
by the attraction of the planets as to pass off in parabo- 
lic curves, to return to our system no more. 

Prof. Nichol is of opinion that the greater number 
visit our system but once ; and then fly off in nearly 
straight lines till they pass the centre of attraction between 
the Solar System and the fixed stars, and go to revolve 
around other suns in the far distant heavens. * Sir 
John Herschel expresses the same sentiment.*)" 

6. The distances to which those comets that return 
must go, to be so long absent, must be very great. Still 
their bounds are set by the great law of attraction, for 
were they to pass the point " where gravitation turns 
the other way," they would never return. But some, at 
least, do return, even from their " long travel of a thou- 
sand years." What a sublime conception this affords us 
of the almost infinite space between the Solar System and 
the fixed stars ! 

7. The direction of comets is as variable as their 
forms and magnitudes. They enter the Solar System 
from all points of the heavens. Some seem to come up 
from the immeasurable depths below the ecliptic, and, 
having doubled heaven's mighty cape, again plunge 
downward with their fiery trains, and are lost for ages 
in the ethereal void. Others appear to come down from 
the zenith of the universe, and having doubled their pe- 
rihelion, reascend far above all human vision. Others, 

* Solar System, p. 135. 

f Treatise, American Ed. p. 289. 



DISTANCES, NUMBER, ETC., OF COMETS. 115 

again are dashing through the Solar System, in all possi- 
ble directions, apparently without any prescribed path, 
or any guide to direct them in their wanderings. In- 
stead of revolving uniformly from east to west, like the 
planets, their motions are direct, retrograde, and in every 
conceivable direction. 

S. The number of comets belonging to, or that visit, 
the Solar System is very great. It is supposed that not 
less than 700 have appeared at different times since the 
birth of Christ. The paths of only about 140 have been 
determined. 

The perihelion distances of the various comets that 
have been noticed, and whose elements have been esti- 
mated by astronomers, are also exceedingly variable. 
While some pass very near the Sun, others are at an 
immense distance from him, even at their perihelion. 
Of 137 that have been particularly noticed, 

30 passed between the Sun and the orbit of Mercury ; 

44 between the orbits of Mercury and Venus ; 

34 " " " Venus and the Earth ; 

23 " " " the Earth and Mars ; 
6 " " " Mars and Jupiter. 

The extreme difficulty of observing comets whose 
nearest point is beyond the orbit of Mars, is supposed to 
account for the comparatively small number that have 
been seen without that limit ; and the proximate unifor- 
mity of the distribution of their orbits over the space 
included within the orbit of Mars, seems to justify the 
conclusion, that though seldom detected beyond his path, 
they are nevertheless equally distributed through all the 
spaces of the solar heavens. Reasoning upon this hy- 
pothesis, Prof. Arago concludes that there are probably 
seven millions of comets that belong to or visit the Solar 
System. * 

9. Comets were formerly regarded as harbingers of 
famine, pestilence, war, and other dire calamities. In 
one or two instances they have excited serious appre- 
hension that the day of judgment was at hand; and that 

* Arago and Lardner's Astronomy, p. 70. 



116 ELEMENTARY ASTRONOMY. 

they were the appointed messengers of Divine wrath, hast- 
ing apace to burn up the world. It may be well, there- 
fore, to devote a paragraph to the question, Are comets 
dangerous in the Solar System ? That they are not will 
be evident when we consider, 

First, that there is scarcely the remotest probability 
of a collision between the earth and a comet. It has 
been determined, upon mathematical principles, and af- 
ter the most mature and extended calculation, that of 
281,000,000 of chances there is only one unfavorable, 
or that can produce a collision between the two bodies. 
The risk, therefore, to which the earth is exposed of being 
struck by a comet, is like the chance one would have 
in a lottery, where there were 281,000,000 black balls 
and but one white one, and where the white ball must be 
produced at the first drawing to secure a prize. 

In the second place, if a comet were to come in direct 
collision with the earth, it is not probable that it would be 
able even to penetrate our atmosphere ; much less to dash 
the world in pieces. Prof* Olmsted remarks, that in 
such an event not a particle of the comet would reach 
the earth — that the portions encountered by her would 
be arrested by the atmosphere, and probably inflamed ; 
and that they would perhaps exhibit on a more magnifi- 
cent scale than was ever before observed, the phenome- 
na of shooting stars, or meteoric showers. * The idea, 
therefore, that comets are dangerous visitants to our 
system has more support from superstition than from rea- 
son or science. 

I cannot better conclude this chapter than in the 
language of the lamented Burritt : " What regions these 
bodies visit, when they pass beyond the limits of our 
view ; upon w r hat errands they come, when they again 
revisit the central parts of our system ; what is the 
difference between their physical constitution and that 
of the Sun and planets ; and what important ends they 
are destined to accomplish in the economy of the uni- 
verse, are inquiries which naturally arise in the mind, 

* Introduction to Astronomy, p. 274. 



GENERAL REMARKS RESPECTING THE SUN. 117 

but which surpass the limited powers of the human un- 
derstanding at present to determine." 



CHAPTER VII. 

OF THE SUN. 
LESSON XCIX. 

GENERAL REMARKS RESPECTING THE SUN— ITS MAGNI- 
TUDE, ETC. 

(Map 4.) 

Although it has been found necessary to give many- 
interesting facts respecting the Sun, in the preceding 
lessons, it is thought important to repeat them here, with 
others, in a more systematic order ; and with opportunity 
for descriptions and explanations more in detail. 

Of all the celestial objects with which we are ac- 
quainted, none make so strong and universal an impres- 
sion upon our globe as does the Sun. He is the great 
centre of the Solar System — a vast and fiery orb, kindled 
by the Almighty on the morn of creation, to cheer the 
dark abyss, and to pour his radiance upon surrounding 
worlds. Compared with him, all the solar bodies are of 
inconsiderable dimensions ; and without him, they are 
wrapped in the pall of interminable midnight. 

The Sun is 886,000 miles in diameter. Were a 
tunnel opened through his centre, and a railway laid 
down, it would require, at the rate of thirty miles per 
hour, nearly three and a half years for a train of cars to 
pass through it. To traverse the whole circumference of 
the Sun, at the same speed, would require nearly eleven 
years. His diameter is 112 times that of the Earth, and 
his mass 1,400,000 times as great. He is 500 times 
larger than all the rest of the Solar System put together. 
The mean diameter of the Moon's orbit is 480,000 
miles ; and yet were the Sun to take the place of the 
Earth, he would fill the entire orbit of the Moon, and 



118 ELEMENTARY ASTRONOMY. 

extend more than 200,000 miles beyond it on every 
side. 

The form of the Sun is that of a spheroid ; his equa- 
torial being somewhat greater than his polar diameter. 
The map referred to exhibits the relative diameters of 
the Sun and Planets. 



LESSON C. 

SPOTS ON THE SUN 5 S SURFACE THEIR NUMBER. 

(Map 4.) 

By the aid of telescopes a variety of spots are often 
discovered upon the Sun's disc. Their number is ex- 
ceedingly variable at different times. From 1611 to 
1629, a period of 18 years, the Sun was never found 
clear of spots, except for a few days in December, 1624. 
At other times twenty or thirty were frequently seen at 
once ; and at one period, in 1825, upwards of fifty were 
to be seen. Prof. Olmsted states that over one hundred 
are sometimes visible. From 1650 to 1670, a period of 20 
years, scarcely any spots were visible ; and for eight years, 
from 1676 to 1684, no spots whatever were to be seen. 
For the last 46 years more or less spots have been visible 
every year. For several days, during the latter part of 
September, 1846, I could count sixteen which were dis- 
tinctly visible, and most of them well defined ; but on 
the 7th of October following, only six small spots were 
visible, though the same telescope was used, and circum- 
stances were equally favorable. 



LESSON CI. 

REVOLUTION OF THE SUN UPON HIS AXIS. 

(Map 4.) 

The axis of the Sun is inclined to the ecliptic 7£°, 
or more accurately 7° 20 7 . This is but a slight devia- 



DIRECTION, MOTIONS, ETC., OF THE SOLAR SPOTS. 119 

tion from what we may call a perpendicular, so that in 
relation to the Earth, he may be considered as standin 
up and revolving with one of his poles resting upon a 
point just half his diameter below the ecliptic. The 
proof of his revolution is the same as that by which we 
determine the revolution of the planets ; namely, the 
passage of spots over his disc. The time occupied in a 
complete revolution is 25 days 10 hours. 



LESSON CII. 

MAGNITUDE OF THE SOLAR SPOTS. 

(Map 4.) 

The magnitude of the solar spots is as variable as 
their number. Upon this point the map will give a cor- 
rect idea ; as it is a pretty accurate representation of 
the Sun's disc, as seen on the 22d of September, 1846. 
In 1799, Dr. Herschel observed a spot nearly 30,000 
miles in breadth ; and he further states, that others have 
been observed whose diameter was upwards of 45,000 
miles. Dr. Dick observes that he has several times 
seen spots which were not less than ^ of the Sun's 
diameter, or 22,192 miles across. 

It is stated, upon good authority, that solar spots have 
been seen by the naked eye — a fact, from which Dr. 
Dick concludes that such spots could not be less than 
50,000 miles in diameter. The observations of the 
writer, as above referred to, and represented on the map, 
would go to confirm this deduction, and to assign a still 
greater magnitude to some of these curious and interest- 
ing phenomena. 

LESSON cm. 

DIRECTION, MOTIONS, AND PHASES OF THE SOLAR SPOTS. 

(Map 4.) 

As the result of the Sun's motion upon his axis, his 
spots always appear first on his eastern limb, and pass off 



120 ELEMENTARY ASTRONOMY. 

or disappear on the west. During one half of their pas- 
sage across his disc, their apparent motion is accelerated ; 
and during the remainder it is retarded. 

This apparent irregularity in the motion of the spots 
upon the Sun's surface, is the necessary result of an 
equable motion upon the surface of a globe or sphere. 
When near the eastern limb, the spots are coming partly 
towards us, and their angular motion is but slight ; but 
when near the centre, their angular and real motions 
are equal. So, also, as the spots pass on to the west, it 
is their angular motion only that is diminished, while the 
motion of the Sun upon his axis is perfectly uniform. 

The figure of the Sun affects not only the apparent 
velocity of the spots, but also their forms. When first 
seen on the east they appear narrow and slender, as 
represented on the left of Fig. 1. As they advance 
westward, they continue to widen or enlarge till they 
reach the centre, where they appear largest, when they 
again begin to contract, and are constantly diminished 
till they disappear. 

Another result of the figure of the Sun, together with 
his revolution upon an axis inclined to the ecliptic, and 
the revolution of the Earth around him, is, that when 
viewed from our movable observatory, the Earth, at 
different seasons of the year, the direction of the spots 
seems materially to vary. This fact is illustrated by Fig. 
2. In June we have, so to speak, a side view of the 
Sun, his pole being inclined to the left. Of course, then, 
as he revolves, his spots will appear to ascend in a straight 
line. In September we have passed around in our orbit, 
to a point opposite the south pole of the Sun, and the 
spots seem to curve upward. In December we have 
another side view of the Sun, but we are opposite the 
point from which we had our first view, and on the other 
side of the ecliptic. The result is, that the poles of the 
Sun are now inclined to the right ; and the spots, in 
passing over his disc, incline downward. In March, we 
reach a point opposite the south pole of the Sun, and the 
spots in revolving seem to curve downward. The polar 
inclination of the Sun, as given in the figure, is greater 



SUPPOSED NATURE AND CAUSES OF THE SOLAR SPOTS. 121 

than it actually is in nature (see Lesson XLIX. and Map 
8) ; the present design being merely to illustrate the 
principle upon which we account for the peculiar mo- 
tion of the solar spots* 



LESSON CIV. 

SUPPOSED NATURE AND CAUSES OF THE SOLAR SPOTS. 

(Map 4.) 

The appearance of the spots is that of a dark nucleus 
surrounded by a border less deeply shaded, called a pe- 
numbra. These appearances are represented on the map. 

When seen through a telescope, the Sun presents the 
appearance of a vast globe, wrapped in an ocean of flame, 
with the spots, like incombustible islands, floating in the 
fiery abyss. The principal facts by which we are to 
judge of their nature and causes are the following: 

1. The Sun is often entirely destitute of spots. 

2. When they are to be seen, the same spots do not 
regularly reappear on the east and pass around, with 
every successive revolution, to the west. 

3. They are exceedingly variable as to number and 
magnitude. 

4. They have been known to break hi pieces and di- 
vide ; and even finally to disappear altogether in a very 
short time. 

5. They sometimes break out again, in the same 
places ; and new ones often break out where none were 
perceptible before. 

6. When they disappear, the central dark spot always 
contracts into a point, and vanishes before the penumbra 
or border disappears. 

7. In the neighborhood of the large spots, the surface 
of the Sun is'covered with strongly marked streaks or 
arms, more luminous than the rest, called faculce, among 
which the spots often break out. The dark spots are 
sometimes called macula. 



122 ELEMENTARY ASTRONOMY. 

8. The spots are all found within 30° of the Sun's 
equator, or in a zone of 60° in width. 

9. In a series of experiments conducted by Prof. 
Henry, of Princeton, by means of a thermo-electrical 
apparatus, applied to an image of the Sun thrown on a 
screen from a dark room, it was found that the spots 
were perceptibly colder than the surrounding light sur- 
face. 

Concerning these wonderful spots a variety of opinions 
have prevailed, and many curious theories have been 
constructed. Lalande, as cited by Herschel, suggests 
that they are the tops of mountains on the Sun's surface, 
laid bare by fluctuations in his luminous atmosphere ; 
and that the pen umbrae are the shoaling declivities of 
the mountains, where the luminous fluid is less deep. 
Another gentleman, of some astronomical knowledge, 
supposes that the tops of the solar mountains are exposed 
by tides in the Sun's atmosphere, produced by planetary 
attraction. 

To the theory of Lalande, Dr. Herschel objects that 
it is contradicted by the sharp termination of both the in- 
ternal and external edges of the penumbrse ; and advances 
as a more probable theory, that " they are the dark, or 
at least comparatively dark, solid body of the Sun itself, 
laid bare to our view by those immense fluctuations in 
the luminous regions of the atmosphere, to which it ap- 
pears to be subject." Prof. Olmsted supports this theory 
by demonstrating that the spots must be " nearly or quite 
in contact with the body of the Sun." 

In 1773, Prof. Wilson, of the University of Glasgow, 
ascertained by a series of observations that the spots 
were probably " vast excavations in the luminous matter 
of the Sun ; " the nuclei being their bottom, and the 
umbras their shelving sides.* This conclusion varies 
but little from that of Dr. Herschel, subsequently arrived 
at.f 

* A valuable paper upon the subject of the solar spots, written 
by the lamented Ebenezer Porter Mason, may be found in his excel- 
lent Memoir, by Prof. Olmsted, page 238. 

+ Nichol's Solar System, pp. 122— 126. 



PHYSICAL CONSTITUTION OF THE SUN. 123 

LESSON CV. 

PHYSICAL CONSTITUTION OF THE SUN. 

Concerning the physical organization of the Sun, 
very little is known. As before said, it appears when 
seen through a telescope, like a globe of fire, in a 
state of violent commotion or ebullition. La Place be- 
lieved it to be in a state of actual combustion, the spots 
being immense caverns or craters, caused by eruptions 
or explosions of elastic fluids in the interior. 

The most probable opinion is that the body of the 
sun is opaque, like one of the planets ; that it is sur- 
rounded by an atmosphere of considerable depth ; and 
that the light is sent off from a luminous stratum of 
clouds, floating above or outside the atmosphere. This 
theory accords best with his density, and with the phe- 
nomena of the solar spots. 

Of the temperature of the Sun's surface, Dr. Herschel 
thinks that it must exceed that produced in furnaces, or 
even by chemical or galvanic processes. By the law rela- 
tive to the diffusion of light (Lesson XII.) he shows that 
a body at the Sun's surface must receive 300,000 times 
the light and heat of our globe ; and adds that a far less 
quantity of solar light is sufficient, when collected in the 
focus of a burning-glass, to dissipate gold and platina 
into vapor. And yet this theory of the high tempera- 
ture at the Sun's surface, is thought by some philoso- 
phers to be no barrier in the way of its habitability. 

It is supposed that the luminous matter is of less 
specific gravity than the vapor and clouds in the Sun's 
atmosphere ; and that these, together with the atmos- 
phere, form an effective screen against the excessive 
solar radiation. 

After all, it must be confessed that but little is known 
as yet of the nature of this wonderful orb. For his 
density and attractive force, see Lessons XVI. and XVII. 



124 ELEMENTARY ASTRONOMY. 

LESSON CVL 

THE ZODIACAL LIGHT. 

The Zodiacal Light is a faint nebulous light, resem- 
bling the tail of a comet, or the milky-way, which seems 
to be reflected from the regions about the Sun ; and is 
distinguishable from ordinary twilight. Its form is that 
of a pyramid or cone, with its base towards the Sun, and 
inclined slightly to the ecliptic. It seems to surround 
the Sun on all sides, though at various depths, as it may 
be seen in the morning preceding the Sun, as well as in 
the evening following him ; and the base of the cones 
where they meet at the Sun, must be much larger than 
his diameter. 

The form of this substance surrounding the Sun, and 
which is sufficiently dense to reflect his light to the 
earth, seems to be that of a lens ; or rather like a huge 
wheel, thickest at the centre, and thinned down to an 
edge at the outer extremities. Its being seen edgewise, 
and only one half at a time, gives it the appearance of 
two pyramids with their bases joined at the Sun. 

Of the nature of this singular phenomenon very little 
is positively known. It was formerly thought to be the 
atmosphere of the Sun. Prof. Nichol says : " Of this at 
least we are certain — the Zodiacal Light is a phenom- 
enon precisely similar in kind to the nebulous atmos- 
pheres of the distant stars," &c. Sir John Herschel 
remarks, that " it is manifestly of the nature of a thin 
lenticularly-formed atmosphere, surrounding the Sun, 
and extending at least beyond the orbit of Mercury, and 
even of Venus." He gives the apparent angular dis- 
tance of its vertex from the Sun, at from 40° to 90° ; 
and the breadth of its base from 8° to 30°. It sometimes 
extends 50° westward, and 70° eastward of the Sun at 
the same time. 

In regard to its atmospheric character, Dr. Dick re- 



THE ZODIACAL LIGHT. , 125 

marks that "this opinion now appears extremely du- 
bious ;" and Prof. Olmsted refers to La Place, as show- 
ing that the " solar atmosphere could never reach so far 
from the Sun as this light is seen to extend." 

Another class of astronomers suppose this light, or 
rather the substance reflecting this light, to be some of 
the original matter of which the Sun and planets were 
composed — a thin nebulous substance in a state of con- 
densation, and destined either to be consolidated into new 
planetary worlds, during the lapse of coming ages, or to 
settle down upon the Sun himself as a part of his legiti- 
mate substance. This theory may be noticed again 
when we come to speak of Nebulse and Nebulous Stars, 
in the second part of this work. 

Prof. Olmsted supposes the Zodiacal Light to be a 
nebulous body, or a thin vapory mass revolving around 
the Sun ; and that the Meteoric Showers, which have 
occurred for several years, in the month of November, 
may be derived from this body. This is the opinion of 
Arago, Biot, and others. 

The best time for observing the Zodiacal Light is on 
clear evenings, in the months of March and April. It 
may be seen, however, in October, November, and 
December, before sunrise ; and also in the evening sky. 

It is an interesting fact, stated by Prof. Nichol, that 
this light, or nebulous body, lies in the plane of the 
Sun's equator. A line drawn through its transverse 
diameter, or from one apex of the pyramids to the other, 
would cross the axis of the Sun at right angles. This 
fact would seem to indicate a revolution with that of the 
Sun upon his axis. 

But, as already stated, the subject of the Zodiacal 
Light is in an unsettled state. After considering the 
various facts and theories stated, the learner must wait 
till future observations and discoveries shall furnish 
something upon this point more definite and satisfactory. 



126 ELEMENTARY ASTRONOMY. 

LESSON CVII. 

MOTION OF THE SUN IN SPACE. 

Although in general terms we speak of the Sun as the 
fixed centre of the Solar System, still the sublime and 
astonishing fact has been ascertained, that the Sun, and 
the whole Solar System, have an actual motion in space. 
Indeed the Sun may be said to have three distinct mo- 
tions. 

1. It has a revolution upon its own axis, once in 25 
days 9^ hours, as described in Lesson XXXVII. 

2. " It has a periodical motion, in nearly a circular 
direction, around the common centre of all the planetary 
motions ; never deviating from its position by more than 
twice its diameter." From the known laws of gravita- 
tion, it is certain that the Sun is affected in some measure 
by the attraction of the planets, especially when many of 
them are found on the same side of the ecliptic at the same 
time ; but this would by no means account for so great a 
periodical motion. 

3. It is found to be moving, with all its retinue of 
worlds, in a vast orbit, around some distant and un- 
known centre. This opinion was first advanced, I think, 
by Sir William Herschel ; but the honor of actually 
determining this interesting fact belongs to Struve, who 
ascertained not only the direction of the Sun and Solar 
System, but als their velocity. The point of tendency 
is towards the ° constellation of stars called Hercules, 
Right Ascension 259°, Declination 35°. See Lessons 
XLVII. XLVI1I. The velocity of the Sun, &c, in space, 
is estimated at about 28,000 miles per hour, or nearly 
8 miles per second ! 

With this wonderful fact in view, we may no longer 
consider the Sun as fixed and stationary, but rather as a 
vast and luminous planet, sustaining the same relation to 
some central orb, that the primary planets sustain to him, 
or that the secondaries sustain to their primaries. Nor 
is it necessary that the stupendous mechanism of nature 



NEBULAR THEORY OF THE ORIGIN OF SOLAR SYSTEM. 127 

should be restricted even to these sublime proportions. 
The Sun's central body may also have its orbit, and its 
centre of attraction and motion, and so on, till, as Dr. 
Dick observes, we come to the great centre of all — to the 
Throne of God. 

The Sun will be further considered as a Fixed Star, 
in Part II. 



CHAPTER VIII. 

MISCELLANEOUS REMARKS UPON THE SOLAR 
SYSTEM. 

LESSON CVIII. 

NEBULAR THEORY OF THE ORIGIN OF THE SOLAR SYSTEM. 

It is the opinion of La Place, a celebrated French 
astronomer, that the entire matter of the Solar System, 
which is now mostly found in a consolidated state, in 
the Sun and Planets, was once a vast nebula, or 
gaseous vapor, extending beyond the orbits of the most 
distant planets — that in the process of gradual condensa- 
tion, by attraction, a rotary motion was engendered and 
imparted to the whole mass — that this motion caused the 
consolidating matter to assume the form of various con- 
centric rings, like those of Saturn ; and, finally, that 
these rings, collapsing, at their respective distances, and 
still retaining their motion, were gathered up into planets, 
as they are now found to exist. This opinion is supposed 
to be favored, not only by the fact of Saturn's revolving 
rings, but by the existence of the Zodiacal Light, or a 
resisting medium about the Sun (CVI.), and also by the 
character of irresolvable or planetary nebulae, hereafter 
to be described. 

On the other hand, the nebular theory is open to 
many very plausible objections. But we have not room 



128 ELEMENTARY ASTRONOMY. 

in this treatise to enter at length upon its discussion. It 
is but justice, however, to say, that men eminent for 
learning and piety have advocated it, in the belief that it 
was perfectly consistent with the Mosaic account of the 
creation of the heavens and the earth. If the opinion of 
the writer is desired, he is frank to state, that while he 
acknowledges the force of some of the considerations 
urged in its support, he has not yet seen reason for 
adopting the nebular theory of the formation of the Solar 
System. 

LESSON CIX. 

LAW'S OF PLANETARY MOTION. 

There are three general principles which govern the 
motions of all the planets. These were first discovered 
by Kepler, a German astronomer, from whom they have 
since been called Kepler's laws. These laws or princi- 
ples we have not time to explain in detail ; nevertheless, 
they are inserted here for the benefit of advanced pupils, 
who may wish to make calculations upon them, when 
the easier lessons of the work are all fully mastered. 
They are as follows : 

1. The orbits of the Earth, and all the Planets, are eh 

lipses, having the Sun in the common focus. 

2. The radius vector, (or line drawn from the centre of the 

Sun to any Planet revolving around it,) describes 
equal areas in equal times. 

3. The squares of the periodic times are as the cubes of 

the mean distances from the Sun. 

According to these laws, which are known to prevail 
in the Solar System, many of the facts of astronomy are 
deduced from other facts previously ascertained. They 
are, therefore, of great importance, and should be studied 
till they are, at least, thoroughly understood, if not com- 
mitted to memory. The first is illustrated in several of 



MINIATURE REPRESENTATION OF THE SOLAR SYSTEM. 129 

the maps, and the ingenious teacher will readily illustrate 
the second by a simple diagram upon a slate or black- 
board. It would be a very useful exercise for the pupil 
to test the table in which the distances and periodic times 
are given, by this third law. See Lessons VIII. and 
XVIII. 

LESSON CX. 

MINIATURE REPRESENTATION OF THE SOLAR SYSTEM. 

At the close of his remarks on the Primary Planets,* 
Sir John Herschel, has a most graphic and interesting 
description of the Solar System in miniature, which is 
here inserted for the perusal of the learner. 

Choose any well levelled field or bowling-green. On 
it place a globe two feet in diameter ; this will represent 
the Sun ; Mercury will be represented by a grain of 
mustard seed, on the circumference of a circle 164 feet 
in diameter for its orbit ; Venus a pea, on a circle 284 
feet in diameter ; the Earth also a pea, on a circle of 
430 feet ; Mars a rather large pin's head, on a circle of 
654 feet ; Vesta, Juno, Ceres, and Pallas, [also Astrsea,] 
grains of sand, in orbits of 1000 to 1200 feet ; Jupiter a 
moderate sized orange, on a circle nearly half a mile 
across ; Saturn a small orange, on a circle of four-fifths 
of a mile ; and Herschel a full sized cherry, or small 
plum, upon a circumference of a circle more than a mile 
and a half in diameter. ***** 

To imitate the motions of the planets, in the above 
mentioned orbits, Mercury must revolve in its orbit 
in 41 seconds ; Venus in 4 min. 14 sec. ; the Earth 
in 7 min. ; Mars in 4 min. 48 sec. ; Jupiter in 2 h. 
56 min. ; Saturn in 3 h. 13 min. ; and Herschel in 2 h. 
16 min. 

So far as relative magnitude is concerned, it will be 
easy to discover the general accuracy of Maps 2 and 4, 
according to the representations of Dr. Herschel, as 

* Treatise, p. 271. 

7+ 



130 ELEMENTARY ASTRONOMY. 

above quoted. It is proper, however, to add, that the 
maps were calculated by the author without any refer- 
ence to the foregoing, or any recollection of its existence. 



LESSON CXI. 

WERE THE ASTEROIDS ORIGINALLY ONE PLANET ? 

1. Some very curious speculations have been enter- 
tained by astronomers in regard to the origin of the As- 
teroids. As in the case of the recently discovered planet 
Leverrier, the existence of a large planet between the 
orbits of Mars and Jupiter was suspected before the As- 
teroids were known. This suspicion arose mainly from 
the seeming chasm that the absence of such a body would 
leave in the otherwise well-balanced Solar System. 

2. The prediction that such a body would be discov- 
ered in the future, stimulated the search of astronomers, 
till, at length, instead of one large planet, jive small ones 
were one after another discovered. For the time of their 
discovery, &c, see Lesson LXV. 

3. From certain peculiarities of the Asteroids, it has 
been considered highly probable that they were origin- 
ally one large planet, which had been burst asunder by 
some great convulsion or collision, and of which they 
are the fragments. The grounds of this opinion are as 
follows : 

(1.) The Asteroids are smaller than any of the other 
primary planets. Lesson XIV. 

(2.) Their distances from the Sun are nearly the 
same, as will be seen in Lesson VIII. 

(3.) Their periodic revolutions are accomplished in 
nearly the same time, as appears by Lesson XVIII. The 
difference of their periodic times is not greater than 
might result from the supposed disruption, as the parts 
thrown forward would have their motion accelerated, 
while the other parts would be thrown hack or retarded ; 
thus changing the periodic times of both. 

(4.) The great departure of the orbits of the Asteroids 



WERE THE ASTEROIDS ORIGINALLY ONE PLANET ? 131 

from the plane of the ecliptic is supposed to favor the hy- 
pothesis of their having been originally one planet. 

(5.) Their orbits are more eccentric than those of the 
other primaries, as may be seen in Lesson XLV. Al- 
though the table shows the eccentricity of Herschel's 
orbit as greater in miles than that of even Juno or Pallas, 
yet when we consider the difference in the magnitude of 
their orbits, it will easily be seen that his orbit is less 
elliptical than theirs. 

(6.) The orbits of Ceres and Pallas, at least, cross 
each other, as shown in Map 2. This, if we except the 
comets, is a perfect anomaly in the Solar System. 

From all these circumstances, it has been concluded 
that the Asteroids are only the fragments of an exploded 
world, which have assumed their present forms since the 
disruption, in obedience to the general laws of gravita- 
tion. This theory of Dr. Olbers, is favored by Prof. 
Nichol, Dr. Brewster, Dr. Dick, and others; while Sir 
John Herschel observes that it may serve as a specimen 
of the dreams in which astronomers, like other specula- 
tors, occasionally and harmlessly indulge.* Dr, Dick 
remarks, that the breaking up of the exterior crust of the 
Earth, at the time of the general deluge, was a catas- 
trophe as tremendous and astonishing as the bursting 
asunder of a large planet. f 

The late General Root, of Delhi, was of opinion that the 
Asteroids were primarily satellites of Mars ; which, as 
if dissatisfied with their low condition as mere attendants 
upon another, and one, too, not much larger than thercu 
selves, have wandered from their original spheres, and as- 
sumed the character of primaries. The reasons for this 
opinion, as stated to the author by Gen. Root, in the fall of 
1846, are quite as satisfactory as the evidences by which 
the theory of Dr. Olbers is supported. But this is not en- 
dorsing either the one or the other. Indeed, in view of 
the harmony and order that reign throughout the plan- 
etary regions, directing the pathway and controlling the 
destiny of every world, it is hard to believe that any 

* Treatise, p 162. t Celestial Scenery., p. 140. 



132 ELEMENTARY ASTRONOMY. 

planet has either been broken to pieces by some mighty 
explosion or concussion, or wandered from its prescribed 
path into a new and vastly extended orbit, 



LESSON CXII. 

ARE THE PLANETS INHABITED BY RATIONAL BEINGS? 

Upon this interesting question, it must be admitted, 
that we have no positive testimony. The argument in the 
affirmative is based upon analogies, and the conclusion is 
to be regarded only in the light of a legitimate inference. 
Still, it is remarkable that those who are best acquainted 
with the facts of astronomy are most confident that other 
worlds, as well as ours, are the abodes of intellectual 
life. Indeed, as Dr. Dick well remarks, it requires a 
minute knowledge of the whole scenery and circum- 
stances connected with the planetary system, before this 
truth comes home to the understanding with full con- 
viction. 

It is not proposed, in this lesson, to discuss at length 
the question of a plurality of worlds, but merely to give 
the heads of the arguments by which this doctrine is 
supported, leaving the reader to amplify them by reflec- 
tion, or to pursue the inquiry, at his leisure, in more 
elaborate works. Perhaps no writer has done better jus- 
tice to this subject lhan Dr. Dick,* to whom we are in- 
debted for many of the arguments with which this lesson 
is enriched. 

1. The planets are all solid bodies resembling the 
Earth, and not mere clouds or vapors. 

2. They all have a spherical or spheroidal figure , 
like our own planet. 

3. The laws of gravitation, by which we are kept 
upon the surface of the Earth, prevail upon all the other 
planets, as if to bind races of material beings to their 
surfaces, and provide for the erection of habitations and 
other conveniences of life. 

* Celestial Scenery, pp. 331-363. 



ARE THE PLANETS INHABITED I 133 

4. The magnitudes of the planets are such as to afford 
ample scope for the abodes of myriads of inhabitants. It 
is estimated that the solar bodies, exclusive of the comets, 
contain an area of 78,000,000,000 of square miles ; or 
397 times the surface of our globe. According to the 
population of England, this vast area would afford a resi- 
dence to 21,875,000,000,000 of inhabitants ; or 27,000 
times the population of our globe. 

5. The planets have a diurnal revolution around 
their axes, thus affording the agreeable vicissitudes of 
day and night. Not only are they opaque bodies like 
our globe, receiving their light and heat from the Sun, 
but they also revolve so as to distribute the light and 
shade alternately over all their surfaces. There, too, 
the glorious Sun arises, to enlighten, warm, and cheer ; 
and there " the sun-strown firmament " of the more dis- 
tant heavens is rendered visible by the no less important 
blessing of a periodic night. 

It is very remarkable, also, that those planets whose 
bulks are such as to indicate an insupportable attractive 
force, are not only less dense than our globe, but they 
have the most rapid daily revolution \ as if by diminished 
density, and a strong centrifugal force combined, to re- 
duce the attractive force, and render locomotion possible 
upon their surfaces. 

6. All the planets have an annual revolution round 
the Sun; which, in connection with the inclination of 
their axes to their respective orbits, necessarily results in 
the production of seasons. 

7. The planets, in all probability, are environed 
with atmospheres. That this is the case with many of 
them is certain ; and the fact that a fixed star or any 
other orb is not rendered dim or distorted when it ap- 
proaches their margin, is no evidence that the planets 
have no atmosphere. This appendage to the planets is 
known to vary in density ; and in those cases where it 
is not detected by its intercepting or refracting the light, 
it may be too clear and rare to produce such phenomena. 

8. The principal primary planets are provided with 
moons or satellites, to afford them light in the absence of 



134 ELEMENTARY ASTRONOMY. 

the Sun. It is not improbable that both Mars and Venus 
have each, at least, one moon ; the Earth has one ; and 
as the distances of the planets are increased, the number 
of moons seems to increase. The discovery of only six 
around Herschel is no evidence that others do not exist 
which have not yet been discovered. 

9. The surfaces of all the planets, primaries as well 
as secondaries, seem to be variegated with hill and dale, 
with mountain and plain. 

It is also argued, that as every part of the globe we 
inhabit is destined to the support of animated beings, it 
would be contrary to the analogy of nature, as displayed 
to us, to suppose that the other planets are empty and 
barren wastes, utterly devoid of animated being. The 
inquiry presses itself upon the mind with irresistible 
force, Why should this one small world be inhabited, and 
all the rest unoccupied ? For what purpose were all 
these splendid and magnificent worlds fitted up if not to 
be inhabited ? Why these days and years — this light 
and shade — these atmospheres, and seasons, and satel- 
lites, and hill and dale ? The legitimate, and almost in- 
evitable conclusion is, that our globe is only one of the 
many worlds which God has created to be inhabited, and 
which are now the abodes of his intelligent offspring. It 
is revolting to suppose that we of Earth are the only in- 
telligent subjects of the " Great King," whose dominions 
border upon infinity. 



CLASSIFICATION OF THE STARS. , 135 

PART II. 

THE SIDEREAL HEAVENS. 
CHAPTER I. . 

OF CONSTELLATIONS OF STARS. 
LESSON CXIII. 

DISTINGUISHING CHARACTERISTICS OF THE FIXED STARS. 

The Sidereal Heavens embrace all those celestial 
bodies that lie around and beyond the Solar System, in 
the region of the Fixed Stars. 

The Fixed Stars are distinguished from the Solar 
Bodies by the following characteristics : 

1 . They shine by their own light, like the Sun, and 
not by reflection. 

2. To the naked eye they seem to twinkle or scintil- 
late ; while the planets appear tranquil and serene. 

3. They maintain the same general positions with 
respect to each other, from age to age. 

4. They are inconceivably distant, so that when 
viewed through a telescope they present no sensible disc, 
but appear only as shining points on the dark concave of 
the sky. 

To these might be added several other peculiarities 
which will be noticed in the sequel, but they are not ne~ 
cessary to our present purpose. 

LESSON CXIV. 

CLASSIFICATION OF THE STARS, 

(Map 16.) 

For purposes of convenience in finding or refer- 
ring to particular stars, recourse is had to a variety of 



186 ELEMENTARY ASTRONOMY. 

artificial methods of classification, with which the pupil 
should here become acquainted. 

1. The whole concave of the heavens is divided into 
sections of greater or less extent, called Constellations. 
For the origin of these most unnatural and arbitrary di- 
visions consult Lesson XXXVI. A list of the constella- 
tions will be found in a subsequent chapter. 

2. The stars are all classed according to their mag- 
nitudes. There are usually reckoned twelve different 
magnitudes, of which the first six only are visible to the 
naked eye, the rest being telescopic stars. This magni- 
tude, of course, relates only to their apparent brightness, 
as the faintest star may appear dim solely on account of 
its immeasurable distance. 

Fig. A on the map is a representation of the first 
eight magnitudes, the two smallest of which will be in- 
visible to the pupil at a distance. " It must be observed," 
says Dr. Herschel, " that this classification into magni- 
tudes is entirely arbitrary. Of a multitude of bright 
objects, differing, probably, intrinsically both in size and 
in splendor, and arranged at unequal distances from us, 
one must of necessity appear the brightest ; the one next 
below it brighter still, and so on." 

3. The next step is to classify the stars of each con- 
stellation according to their magnitude in relation to each 
other, and without reference to other constellations. In 
this classification the Greek alphabet is first used. For 
instance, the largest star in Taurus would be marked («) 
Alpha ; the next largest (/5) Beta ; the next (/) Gamma, 
&c. When the Greek alphabet is exhausted, the Ro- 
man or English is taken up ; and when these are all 
absorbed, recourse is finally had to figures. 

4. To aid still further in finding particular stars, and 
especially in determining their numbers, and detecting 
changes, should any occur, astronomers have constructed 
catalogues of the stars, one of which is near 2000 years 
old. 

5. Several of the principal stars have a specific name 
like the planets ; as Sirius, Aldebaran, Regulus, &c. 

6. Clusters of stars in a constellation sometimes re- 



NUMBER OF THE FIXED STARS. 



137 



ceive a specific name, as the Pleiades and Hyades in 
Taurus. 

7. The stars are still further distinguished into 
Double, Triple, and Quadruple stars: Binary System; 
Variable Stars ; Periodic Stars ; Nebulous Stars, &c. ; 
all of which will be duly noticed as we proceed. But 
we must first consider the more general divisions of the 
starry heavens. 

LESSON CXV. 

NUMBER OF THE FIXED STARS. 

The actual number of the stars is known only to 
Him who " telleth the number of the stars,' 3 and " calleth 
them all by their names." The powers of the human 
mind are barely sufficient to form a vague estimate of the 
number near enough to be seen by our best telescopes, 
and here our inquiries must end. 

The number of stars down to the twelfth magnitude, 
has been estimated as follows : 



Visible to 
the naked 
eye, 



Visible 
only thro 
tel'scope 



Mi 

Hi 



1st magnitude, 


2d 


a 


3d 


a 


4th 


a 


5th 


a 


6th 


a 


7th 


a 


8th 


u 


9th 


a 


10th 


a 


11th 


a 



1 12th 



18 

52 

177 

376 

1,000 

4,000 

26,000 

170,000 

1,100,000 

7,000,000 

46,000 ; 000 

300,000,000 



5,623 



354,296,000 



Total number, 354,301,623 



138 ELEMENTARY ASTRONOMY. 

Of these stars, Dr. Herschel remarks that from 
15,000 to 20,000 of the first seven magnitudes are al- 
ready registered, or noted down in catalogues ; and Prof. 
Olmsted observes that Lalande has registered the posi- 
tions of no less than 50,000. 

LESSON CXVI. 

DISTANCES OF THE STARS. 

It has been demonstrated that the nearest of the fixed 
stars cannot be less than 20,000,000,000,000 — twenty 
billions of miles distant ! For light to travel over this 
space at the rate of 200,000 miles per second, would 
require 100,000,000 seconds, or upwards of three years. 

What then must be the distances of the telescopic 
stars, of the 10th and 12th magnitudes ? " If we admit," 
says Dr. Herschel, "that the light of a star of each mag- 
nitude is half that of the magnitude next above it, it will 
follow that a star of the first magnitude will require to 
be removed to 362 times its distance, to appear no larger 
than one of the twelfth magnitude. It follows, therefore, 
that among the countless multitude of such stars, visible 
in telescopes, there must be many whose light has taken 
at least a thousand years to reach us ; and that when we 
observe their places, and note their changes, we are, in 
fact, reading only their history of a thousand years' 
date, thus wonderfully recorded." 

Should such a star be struck out of existence now, 
its light would continue to stream upon us for a thousand 
years to come ; and should a new star be created in 
those distant regions, a thousand years must pass away 
before its light could reach the Solar System, to apprise 
us of its existence. 

LESSON CXVII. 

MAGNITUDE OF THE STARS. 

From what we have already said respecting the al- 
most inconceivable distances of the fixed stars, it will 



MAGNITUDE OF THE STARS. . 139 

readily be inferred that they must be bodies of great 
magnitude, in order to be visible to us upon the Earth. 
It is probable, however, that " one star dirTereth from 
another" in its intrinsic splendor or " glory," although 
we are not to infer that a star is comparatively small, 
because it appears small to us. 

The prevailing opinion among astronomers is, that 
what we call the fixed stars are so many Sans, and cen- 
tres of other systems. By a series of experiments upon 
the light received by us from Sirius, the nearest of the 
fixed stars, it is ascertained that if the Sun were removed 
141,400 times his present distance from us, or thirteen 
billions of miles, his light would be no stronger than that 
of Sirius ; and as Sirius is more than twenty billions of 
miles distant, he must, in intrinsic magnitude and splen- 
dor, be equal to two suns like ours. Dr. Wollaston, as 
cited by Dr. Herschel, concludes that this star must be 
equal in intrinsic light to nearly fourteen suns ! 

According to the measurements of Sir Wm. Herschel, 
the diameter of the star Vega in the Lyre, is 38 times 
that of the Sun, and its solid contents 54,872 times 
greater ! 

Sir John Herschel states that while making observa- 
tions with his forty feetjeflector, a star of the first mag- 
nitude was unintentionally brought into the field of view. 
" Sirius," says he, " announced his approach like the 
dawn of day ;" and so great was his splendor when thus 
viewed, and so strong was his light, that the great as- 
tronomer was actually driven from the eye- piece of his 
telescope by it, as if the Sun himself had suddenly burst 
upon his view. He was obliged to employ a colored 
screen, as in the case of solar observations, to protect his 
eye from the strong and glowing radiance. 

According to Sir Wm. Herschel, the relative light of 
the stars of the first six magnitudes is as follows : 

Light of a star of the average 1st magnitude 100 



2d 


a 


25 


3d 


a 


12 


4th 


a 


6 


5th 


a 


2 


6th 


a 


1 



140 ELEMENTARY ASTRONOMY. 

LESSON CXVIII. 

LIST OF THE CONSTELLATIONS. 

Of the nature and origin of the constellations we have 
already spoken in Lesson XXXVI. Their formation 
has been the work of ages. Some of them were known 
at least 3000 years ago, and bore the very names by 
which they are known to this day. In the 9th chapter 
of Job we read of " Arcturus, Orion, and Pleiades, and 
the chambers of the south ;" and in the 38th chapter of 
the same book, it is asked, " Canst thou bind the sweet 
influences of Pleiades, or loose the bands of Orion 1 
Canst thou bring forth Mazzaroth in his season ? or canst 
thou guide Arcturus with his sons ?" 

At first the number of constellations was few. Being 
found convenient in the study of the heavens, new ones 
were added to the list, composed of stars not yet made 
up into hydras and dragons, till there is now scarcely 
stars or room enough left to construct the smallest new 
constellation, in all the spacious heavens. 

The constellations are divided into the Zodiacal, the 
Northern, and the Southern. 

The Zodiacal Constellations are those which lie in the 
Sun's apparent path, or along the line of the Zodiac. 
See Lesson XXXVI. and the map. 

The Northern Constellations are those which lie be- 
tween the Zodiacal and the North Pole of the heavens. 

The Southern Constellations lie between the Zodiacal 
and the South Pole of the heavens. 

The constellations are also distinguished into ancient 
and modern. The following is a list of all the constella- 
tions, both ancient and modern, with the number of prin- 
cipal stars in each, according to Ptolemy's Catalogue, 
and also that of the Observatory Royal of Paris. 



LIST OF THE CONSTELLATIONS. 



141 



I. 



ZODIACAL CONSTELLATIONS. 



Latin names. 


English names. 


Ptol's. 


Ob.R. 


1 °P Aries. 


Tfte .Raw. 


18 


42 


2 « Taurus. 


TAe Bull. 


44 


207 


3 n Gemini. 


The Twins. 


25 


64 


4 25 Cancer. 


The Crab. 


33 


85 


5 SI Leo. 


The Lion. 


35 


93 


6 trg Virgo. 


The Virgin. 


32 


117 


7 =£= Libra. 


The Scale. 


07 


67 


8 TTL Scorpio. 


The Scorpion. 


27 


60 


9 £ Sagittarius. 


The Archer. 


31 


94 


19 V? Capricornus. 


The Goat. 


28 


64 


11 occ Aquarius. 


The Water -hearer. 


45 


117 


12 X Pisces. 


The Fishes. 


38 


116 



II. 



NORTHERN CONSTELLATIONS. 





ancient. 






13 Ursa Minor. 


The Little Bear. 


08 


22 


14 Ursa Major. 


The Great Bear. 


34 


87 


15 Draco. 


The Dragon. 


31 


85 


16 Cepheus. 


Cepheus. 


13 


58 


17 Bootes. 


Bootes. 


23 


70 


18 Corona Borealis. 


The North' n Crown, 


, 08 


33 


19 Hercules. 


Hercules. 


29 


128 


20 Lyra. 


The Harp. 


10 


21 



142 



ELEMENTARY ASTRONOMY. 



Latin names. 


English names, Ptol's. 


Ob. R. 


21 Cygnus. 


The Swan. 


10 


85 


22 Cassiopeia. 


Cassiopeia. 


13 


60 


23 Perseus. 


Perseus. 


29 


65 


24 Auriga. 


The Charioteer. 


14 


69 


25 Ophiuchus. 


The Serpent-bearer. 


29 


61 


26 Sagitta. 


The Arrow. 


05 


18 


27 Aquila. 


The Eagle. 


15 


26 


28 Delphinus. 


The Dolphin. 


10 


19 


29 Equuleus. 


The Little Horse. 


04 


10 


30 Pegasus. 


Pegasus. 


20 


91 


31 Antinous. 


Antinous. 


15 


28 


32 Andromeda. 


Andromeda. 


23 


71 


33 Triang. Borealis. 


The North. Triang. 


04 


15 


34 Coma Berenices. 


Berenice's Hair. 


35 


43 


MODERN. 






35 Leo Minor. 


The Little Lion. 


— 


55 


36 Canes Venatici. 


The Greyhounds. 


— 


38 


37 Sextans. 


The Sextant. 


— 


54 


38 Cerberus. 


Cerberus. 


— 


13 


39 Taurus Poniatowski 


. PoniatowskVs Bull. 


— 


18 


40 Velpecula et Ans. 


The Fox and Goose 


. — 


35 


41 Lacerta. 


The Lizard. 


— 


12 


42 Triangula Minora. 


The Little Triangle 


— 


04 


43 Musca Borealis. 


The Northern Fly. 


— 


05 


44 Tarandus. 


The Rein Deer. 


— 


12 


45 Custos Messium. 


The Harvester. 


— 


07 


46 Camelopardalus. 


The Cameleopard. 


— 


69 


47 Linx. 


The Lynx. 


— 


45 



LIST OF THE CONSTELLATIONS, 



143 



III. 
SOUTHERN CONSTELLATIONS. 





ANCIENT. 






Latin names. 


English names. Ptol's. 


Ob. R. 


48 Cetus. 


The Whale. 


22 


102 


49 Eridanus. 


The River Po. 


34 


85 


50 Orion. 


Orion. 


38 


90 


51 Lepus. 


The Hare. 


12 


20 


52 Canis Minor. 


The Little Bog. 


02 


17 


53 Canis Major. 


The Great Bog. 


29 


54 


54 Argo Navis. 


The Ship Argo. 


45 


117 


55 Hydra. 


The Water Serpent. 


27 


52 


56 Crater. 


The Cup. 


07 


13 


57 Corvtjs. 


The Crow. 


07 


10 


58 Centaurus. 


The Centaur. 


37 


48 


59 Lupus. 


The Wolf. 


19 


34 


60 Ara. 


The Altar. 


07 


08 


61 Corona Australis. 


The South' n Crown. 


13 


12 


62 Piscis Australis. 


The Southern Fish. 

MODERN. 


18 


24 


63 Fornax Chimica. 


The Chemic. Furn. 


— 


39 


64 Reticulis Rhomb. 


The RhomVd Net. 


— 


07 


65 Cela Sculptoria. 


The Engraves Tool. 


— 


15 


66 Dorado vel Xyph. 


The Sword-fish. 


— 


06 


67 CoLUMBA NOACHI. 


The Bove. 


— 


02 


68 Equuleus Pict. 


The P'nter's Easel 


— 


04 


69 Monoceros. 


The Unicorn. 


— 


31 


70 Pyxis Nautica. 


The Marin's Comp. 


— 


14 



144 



ELEMENTARY ASTRONOMY. 



Latin names. 


English names. Ptol's. 


Ob. R. 


71 Autlia Pneumat. 


The Air Pump. — 


22 


72 Avis Solit. 


The Solitary Bird. — 


23 


73 Crux Australis. 


The South'n Cross. — 


06 


74 Muse a Australis. 


The Southern Fly. — 


04 


75 Chameleonis. 


The Chameleon. — 


07 


76 Piscis Volans. 


The Flying Fish. — 


06 


77 Telescopium. 


The Telescope. — 


08 


78 Horologium, 


The Pendulum, SfC. — 


23 


79 Norma Euclidis. 


Euclid's Square. — 


15 


80 ClRCINUS. 


The Compasses. — 


02 


81 Triang. Australis, 


The South. Triang. — 


05 


82 Ap. vel Av. Indica 


The Bird of Parad. — 


04 


83 Mons Mensa. 


Wnt of Table Bay. — 


06 


84 Scutum Sobieski. 


SoMesky's Shield. — 


16 


85 Indus. 


The Indian. — 


04 


86 Pavo. 


The Peacock. — 


11 


87 Octans. 


The Octant. — 


07 


88 Microscopium. 


The Microscope. — 


08 


89 Grus. 


The Crane. — 


12 


90 Touch ana. 


The Amer. Goose. — 


11 


91 Hydrus. 


The Water Snake. — 


08 


92 Apparatus Sculp. 


The Sculp? s Studio. — 


28 


93 Phcenix. 


The Phozniv. — 


11 


RECAPITULATION. 




Zodiacal Constellations, 


12 Principal stars, 


1125 


Northern " 


35 " " 


1531 


Southern " 


46 " " 


1050 



Total, 93 



Total, 3706 



DESCRIPTION OF THE PRINCIPAL CONSTELLATIONS. 145 

LESSON CXIX. 

DESCRIPTION OF SOME OF THE PRINCIPAL CONSTELLATIONS. 

Although this work is designed particularly to illus- 
trate the Mechanism of the Heavens, as displayed in the 
Solar System, we are desirous of furnishing the learner 
with a sufficient guide to enable him to extend his in- 
quiries and investigations, not only to the different classes 
of bodies lying beyond the limits of the Solar System, in 
the far-off heavens, but also to the Constellations as such. 
For this purpose we shall here furnish a brief description 
of the principal constellations visible in the United States, 
or in north latilude, by the aid of which the student will 
be able to trace them with very little difficulty, upon that 
glorious celestial atlas which the Almighty has spread 
out before us. 

These descriptions are partly original, and partly from 
the writings of Olmsted and Burritt. 

ZODIACAL CONSTELLATIONS, 

The Constellations of the Zodiac, succeeding each 
other in regular order eastward, and being more easily 
found on that account than others, should first be studied. 

Aries is a small constellation known by two bright 
stars, about 4° apart, which form the head. The 
brightest is the most northeasterly of the two. 

Taurus will be readily found by the seven stars or 
Pleiades, which lie in his neck. The largest star in 
Taurus is AMebaran, in the Bull's eye, a star of the 
first magnitude, of a reddish color, somewhat resembling 
the planet Mars. Aldeboran, and four other stars in the 
face of Taurus, compose the Hyades. They are so 
placed as to form the letter V. 

8 



146 ELEMENTARY ASTRONOMY. 

Gemini is known by two very bright stars, Castor 
and Pollux, about five degrees apart. 

Cancer is less remarkable than any other constella- 
tion of the Zodiac. It has no stars larger than the third 
magnitude, and is distinguished for a group of small 
stars called the Nebula of Cancer, which is often mis- 
taken for a comet. A common telescope resolves this 
nebula into a beautiful assemblage of bright stars. 

Leo is a large and interesting constellation, contain- 
ing an unusual number of very bright stars. Of these 
Regulus is of the first magnitude, and lies directly in the 
ecliptic. North of Regulus are several bright stars in 
the form of a sickle, of which Regulus is the handle. 
Denebola is a bright star of the second magnitude, in the 
Lion's tail. It is about 25° northeast of Regulus, and 
35° west of Arcturus. 

Virgo extends for some distance from west to east, 
but contains only a few bright stars. Of these, Spica in 
the ear of corn which the Virgin holds in her left hand, 
is a brilliant star of the first magnitude. The rest of 
her principal stars are of the third and fourth magni- 
tudes. 

Libra may be known by its four principal stars, 
forming a quadrilateral figure. The two brightest of 
these constitute the beam of the balance, and the smallest 
is in the top or handle. 

Scorpio is one of the most interesting and splendid of 
the constellations. His head consists of five bright stars, 
forming the arc of a circle, and is crossed by the ecliptic 
near the brightest of the five. Nine degrees southeast 
is the star Antares, of a reddish color, and of the first 
magnitude. A number of small stars that curve around 
towards the east constitute the tail of Scorpio. 

Sagittarius lies next to Scorpio, and may be known 



NORTHERN CONSTELLATIONS. , 147 

by three stars arranged in a curve, to represent the how 
of the Archer, the central star being the brightest, and 
having a bright star directly west of it, forming the head 
of the arrow. 

Capricornus lies northeast of Sagittarius, and may 
be known by two bright stars close together, which con- 
stitute the head. 

Aquarius is represented by the figure of a man 
pouring water out of a vessel. Its four largest stars are 
of the third magnitude. Two of these, which lie in a 
line with the brightest stars in Capricornus, constitute 
the head of the figure. 

Pisces, the last of the Zodiacal constellations, lies 
between Aquarius and Aries. The Southern Fish con- 
sists of 24 visible stars, of which one is of the first mag- 
nitude, two of the third, and five of the fourth. The re- 
maining 16 are smaller. The largest star is situated in 
the mouth of the Fish, and is called Fomalhaut. The 
Northern Fish consists wholly of small stars, and is con- 
nected with the Southern by a series of stars forming a 
crooked line between them. 



LESSON CXX. 

NORTHERN CONSTELLATIONS. 

The Constellations of the Zodiac being first well 
learned, so as to be readily recognized, will facilitate the 
learning of others that lie north and south of them. Let 
us, therefore, review the principal Northern Constella- 
tions, beginning north of Aries and proceeding from west 
to east. 

Andromeda may be known by three stars of the 
second magnitude, situated in a straight line, and extend- 
ing from east to west. The figure is that of a woman, 



148 ELEMENTARY ASTRONOMY. 

with her arms extended, and chained by her wrists to a 
rock. The middle star, of the three just named, is 
situated in her girdle, and is called Mirach. The one 
west of Mirach is in the head of Andromeda, and the 
eastern one, called Almaak, is in her left foot. The star 
in her head is in the Equinoctial Coleur. The three 
largest stars in this constellation are of the second mag- 
nitude. Near Mirach are two stars of the third and 
fourth magnitudes, and the three in a row constitute the 
girdle. 

The loose assemblage of small stars directly south of 
Mirach, are the Northern Fish, already described. 

Perseus lies directly north of the Pleiades, and east 
of Andromeda. The figure is that of a man with a 
sword in his right hand, and the head of Medusa in his 
left. About 18° from the Pleiades is Algol, a star of the 
second magnitude, in the head of Medusa ; and 9° north- 
east of Algol is Algenib, of the same magnitude, in the 
back of Perseus. It has, also, four stars of the third 
magnitude. 

Algol will be mentioned again, under the head of 
Variable Stars. 

Auriga ( The Wagoner) is the figure of a man in a 
declining posture, resting one foot upon the horn of Tau- 
rus. It is north of Taurus and Orion, and directly east 
of Perseus. Capella, the principal star in this constella- 
tion, is one of the most brilliant in the heavens. It is in 
the west shoulder of Auriga, and may be known by a 
small triangle near it, formed by three small stars. 

The Lynx comes next in order, but presents nothing 
particularly interesting, as it contains no stars above the 
fourth magnitude, and even these are scattered over a 
large space north of Gemini, and between Auriga and 
Ursa Major. 

Leo Minor is composed of a few small stars lying 
between the sickle in Leo, and the Great Bear. 



NORTHERN CONSTELLATIONS. 149 

Coma Berenices is a beautiful cluster of small stars, 
north of Denebolis, in the tail of the Lion, and of the 
head of Virgo. It has but one star as large as the fourth 
magnitude. Cor Caroli, or Charles's Heart, is a bright 
star about 12° directly north of Coma Berenices. 

Bootes is the figure of a man with a club in his 
right hand, with which he seems to be driving the Great 
Bear round the pole of the heavens. He is thence called 
the Bear Driver. Arcturus, situated near the left knee, 
is a star of the first magnitude, and of a reddish color. 
He is accompanied by three small stars (his " sons "*), 
which form a triangle a little to the southwest. A star 
of the second magnitude is in the head of the figure, and 
two bright stars of the third magnitude form the shoul- 
ders. 

Corona Borealis (The Crown) is situated between 
Bootes on the west, and Hercules on the east. It con- 
sists of six principal stars, in the form of a wreath or 
crown. 

Alphacca, the largest star of the group, is of the third 
magnitude, and may be known by its position in the 
centre of the crown, as well as by its superior brightness. 

Hercules lies immediately east of the crown, and 
occupies a large space in the Northern hemisphere. 
The figure is that of a giant, with a large club in his 
right hand. The head is towards the south. 

This constellation is thickly set with stars, the 
largest of which is called Rasa7gethi, in the head of the 
figure, and is of the second magnitude. It has nine stars 
of the third magnitude, and nineteen of the fourth. 

Ophiuchus ( The Serpent Bearer) is situated directly 
south of Hercules, with its centre nearly over the equator, 
and nearly opposite to Orion. The figure is that of a 
venerable looking man, grasping a serpent in his hands, 
the head of which consists of three bright stars, situated 
* Job 38 : 32. 



150 ELEMENTARY ASTRONOMY. 

a little south of the crown. The folds of the serpent 
may be traced by a succession of bright stars extending 
for some distance to the east. 

The principal star in Ophiuchus is of the second 
magnitude, and is called Ras Alhague. It is situated in 
the head of the figure, and within 5° of Rasalgethi, in 
the head of Hercules. 

Aquila (The Eagle) is conspicuous for three bright 
stars in its neck, of which the central one, Altair, is a 
brilliant white star of the first magnitude. Antinous lies 
directly south of the Eagle, and north of the head of 
Capricornus. 

Delphinus (The Dolphin) is a beautiful little cluster 
of stars, a little to the east of the Eagle. It may be 
known by four principal stars in the head, of the third 
magnitude, arranged in the figure of a diamond, and 
pointing northeast and southwest. A star of the same 
magnitude, about 5° south, makes the tail. 

Pegasus is a large constellation situated between the 
Dolphin and Eagle, on the west, and Andromeda and 
the Northern Fish, on the northeast. The figure is that 
of a winged horse, in an inverted posture. It may be 
known by four stars about 15° apart, forming a square 
called the square of Pegasus. They are of the second 
and third magnitudes, and one of them, viz. Algenib, has 
already been mentioned as belonging to Perseus. 

The Horse's Head is a small cluster of stars, west 
of the head of Pegasus, and about half way to the Dol- 
phin. It contains ten stars, of which the four principal 
are only of the fourth magnitude. They form a long 
irregular square, the two in the nose being 1° apart, and 
those in the eyes 2-*-°. These four stars are about 1° 
southeast of the diamond in the head of the Dolphin, 



NORTHERN CONSTELLATIONS. , 151 

We now come to notice the constellations around the 
North Pole, and which are always above the horizon in 
northern latitudes, 

Ursa Minor (The Little Bear) is near the north 
pole of the heavens. It consists of the Pole Star, as it is 
called, which forms the extremity of the tail, and six 
other principal stars, three of the third, and four of the 
fourth magnitudes. The seven together are arranged in 
the form of a dipper, with the Pole Star in the end of the 
handle* 

Ursa Major ( The Great Bear) may be known by 
the figure of a larger dipper, which constitutes the hinder 
part of the animal. This dipper, also, is composed of 
seven stars. The first, in the end of the handle, is called 
Benetnash, and is of the second magnitude. The next 
is Mizar, known by a minute star almost touching it, 
called Alcor. This is a double star. The third in the 
handle is Alioih. The first star in the bowl of the 
dipper, at the junction of the handle, isJMegrez. Passing 
to the bottom of the dipper we find Pkad, and Merak, 
while Duhhe forms the rim opposite the handle. Merak 
and Dubhe are called the Pointers ; because they always 
point towards the Pole Star. 

The head of the Great Bear lies far to the west of the 
Pointers, and is composed of numerous small stars ; while 
the feet are severally composed of two small stars, very 
near to each other. 

Draco (The Dragon) compasses a large circuit in tlie 
polar regions. He winds round between the Great and 
Little Bear, and commencing with the tail, between the 
Pointers and Pole Star, it is easily traced by a succession 
of bright stars extending from west to east ; passing under 
Ursa Minor, it returns westward, and terminates in four 
stars which form the head, near the foot of Hercules, 
These four stars are 3°, 4° and 5° apart, so situated as 
to form an irregular square ; the two upper ones being the 
brightest, and both of the second magnitude. 



152 ELEMENTARY ASTRONOMY, 

Cepheus lies east of the breast of Draco, but has no 
stars above the second magnitude. The figure is that of 
a king, crowned, and with a sceptre in his left hand, 
which is extended towards Cassiopeia. 

Cassiopeia is a queen on a throne or chair, with her 
head and body in the Milky Way. The chair is com- 
posed of four stars, which form the legs, and two con- 
stituting the back. Five of these are of the third magni- 
tude. 

Lyra (The Lyre) is distinguished by one of the 
brightest stars in the northern hemisphere. It is situated 
east of Hercules, and between him and the Swan. Its 
largest star is Vega, or Alpha Lyra, and is of the first 
magnitude. It has two others of the second magnitude, 
and several of the fourth. 

Cygnus (The Sivan) is situated directly east of 
Lyra. Three bright stars, which lie along the Milky 
Way, form the body and neck of the Swan ; and two 
others, in a line with the middle one of the three, con- 
stitute the wings. These five stars form a large cross. 

Arided, in the body of the Swan, is a star of the first 
magnitude, and the remaining ones of the constellation 
are of the third and fourth magnitudes. 

Camelopardalus (The Cameleopard) is a large and 
uninteresting field of small stars, scattered between Per- 
seus, Auriga, the head of Ursa Major and the Pole Star. 
Its five largest stars are only of the fourth magnitude, 
the principal of which is in the thigh. The head of the 
animal is near the pole. 

The Lynx also is composed of small stars, scattered 
over a large extent. It lies north of Gemini, and be- 
tween Auriga and Ursa Major. Its three largest stars 
are of the third magnitude. 



SOUTHERN CONSTELLATIONS. , 153 

LESSON CXXI. 

SOUTHERN CONSTELLATIONS. 

The Southern Constellations are comparatively few 
in number, though some of them are very beautiful. 

Cetus (The Whale) is the largest constellation in the 
heavens. It is situated below or south of Aries. It is 
represented with its head to the east, and extends 50° 
east and west, with an average breadth of 20°. 

The head of Cetus may be known by five remarkable 
stars, 4° and 5° apart, and so situated as to form a regu- 
lar pentagon, or five-sided figure. Menkar, of the 
second magnitude, in the nose of the Whale, is the largest 
star in the group, or in the constellation. 

Orion lies south of Taurus, and is one of the most 
conspicuous and beautiful of the constellations. The 
figure is that of a man in the act of assaulting the Bull, 
with a sword in his belt, and a club in his right hand. It 
contains two stars of the first magnitude, four of the 
second, three of the third, and fifteen of the fourth. 
Betelguese forms the right, and Bellatrix the left shoul- 
der. A cluster of small stars form the head. Three 
small stars, forming a straight line about 3° in length, con- 
stitute the belt, called by Job " the Bands of Orion" 
They are sometimes called the Three Kings, because 
they point out the Hyades and Pleiades on the one hand, 
and Sirius on the other. A row of very small stars 
runs down from the belt, forming the sword. These, 
with the stars of the belt, are sometimes called the Ell 
and Yard. 

Mintika, the northernmost star in the belt, is less 
than -£° south of the equinoctial. 

Rigel, a bright star of the first magnitude, is in the 
left foot, 15° south of Bellatrix ; and Saiph, of the third 
magnitude, is situated in the right knee, 8-£° east of 
Rigel. 

8* 



154 ELEMENTARY ASTRONOMY. 

Lepus (The Hare) is directly south of Orion. It 
may be known by four stars of the third magnitude, in 
the form of an irregular square. Zeta, of the fourth 
magnitude, is the first star, situated in the back, and 
about 5° south of Saiph in Orion. About the same dis- 
tance below Zeta are the four principal stars, in the legs 
and feet. 

Columba (Noah's Dove) lies about 16° south of Le- 
pus. It contains but four stars, of which Phaet is the 
brightest. It lies on the right a little higher than Beta, 
the next brightest. This last may be known by a small 
star just east of it. 

Eridanus (The River Po) is a large and irregular 
constellation, very difficult to trace. It is 130° in length, 
and is divided into the Northern and Southern streams. 
The former lies between Orion and Cetus, commencing 
near Rigel in the foot of Orion, and flowing out westerly 
in a serpentine course, near 40°, to the Whale. 

Canis Major lies southeast of Orion, and may be 
readily found by the brilliancy of its principal star Si- 
?*ius. This is the largest of the fixed stars, and is sup- 
posed to be the nearest to the Solar System. 

Canis Minor is a small constellation situated between 
Canis Major and the Twins. It has but two principal 
stars, namely, Procyon of the first magnitude, and Go- 
melza of the second. 

Monoceros (The Unicorn) lies between Canis Major 
and Canis Minor, with its centre directly south of Pro- 
cyon. Its largest stars are of the fourth magnitude. 
Three of these are in the head, 3° and 4° apart. 

Hydra has its head near Procyon, and consists of a 
number of stars of ordinary brightness. Alphard, in the 
heart, is a star of the second magnitude, about 15° south- 



SOUTHERN CONSTELLATIONS. 155 

east of the head. It is an extensive constellation, extend- 
ing from east to west more than 100°. 

Corvus {The Croiv) is represented as standing upon 
the tail of Hydra, south of Coma Berenices. It con- 
tains but nine visible stars, only three of which are as 
large as the third magnitude. 

Argo Navis {The Ship Argo) is a large and splendid 
constellation in the southern hemisphere, but so low 
down in the south that but little of it can be seen in 
the United States. It lies southeast of Canis Major, 
and may be known by the stars in the prow of the 
ship. Markeh, of the third magnitude, is 16° southeast 
of Sirius. Naos and Gamma are of the second mag- 
nitude, and Canopus and Miaplacidus of the first. 

Centaurus is another large southern constellation, 
too low in the south to be traced by an observer in the 
United States. 

Lupus {The Wolf) is next east of Centaurus, south of 
Libra, and is also invisible in northern latitudes. 

Sextans ( The Sextant) consists of a number of very 
small stars, situated between Leo on the north, and 
Hydra on the south. Its largest star is of the fourth 
magnitude, and is situated about 13° south ofReg ulus, 
near the equinoctial. 

Crux {The Cross) is a brilliant little constellation, 
but too far south to be visible to us at the north. It 
consists of four principal stars, namely, one of the first, 
two of the second, and one of the third magnitude. 



156 ELEMENTARY ASTRONOMY. 



CHAPTER II. 

OF DOUBLE, VARIABLE, AND TEMPORARY STARS, 
BINARY SYSTEMS, &c. 

LESSON CXXII. 

OF DOUBLE, TRIPLE, AND MULTIPLE STARS. 
(Map 16.) 

1. Many of the stars which, to the naked eye, appear 
single, are found, when examined by the aid of a teles- 
cope, to consist of two or more stars, in a state of near 
proximity to each other. These are called double stars. 
When three or more stars are found thus closely con- 
nected, they are called triple or multiple stars. They 
are also distinguished as binary, ternary, &c. 

2. Double and triple stars are supposed to be con- 
stituted in two ways: first, by actual contiguity, and 
secondly, where they are only near the same line of 
vision, one of the component stars being far beyond the 
other. In the former case they are said to be 'physically 
double, while in the latter they are only optically double. 

3. The figures from B to F on the map are speci- 
mens of double stars. B is a representation of the 
star Mizar, in the tail of the Great Bear. It may be 
seen double with a good spy-glass. C is a view of Big el 
in Orion. D is the Pole Star, and E the star Castor in 
the Twins. Those under F are merely fancy specimens. 

4. The number of double and multiple stars having 
one member as large as the eighth magnitude, and 
whose components are within 32 y/ of each other, is said 
to be about 6,000. This fact led astronomers to suspect 
a physical connection by the laws of gravitation, and 
also a revolution of star around star, as the planets revolve 
around the Sun. 



OF BINARY AND OTHER SYSTEMS. 157 



LESSON CXXIII. 

OF BINARY AND OTHER SYSTEMS. 
(Map 16.) 

1. By carefully noting the relative distances and 
angular positions of double and multiple stars, for a 
series of years, it has been found that many of them have 
their periodic revolutions around each olher. These, it 
must be remembered, are the double and multiple stars, 
which appear single to the naked eye. Sir W. Her- 
schel noticed about fifty instances of changes in the an- 
gular position of double stars, and the revolution of some 
sixteen of these is considered certain. Their periods 
are from 40 to 1600 years. 

2. Fig. G on the map is a representation of one of 
these Binary Systems, namely, the star Gamma, in the 
Virgin. The largest star will be seen in the upper foci 
of the supposed orbit, and the arrows show the direction 
of the revolving star. At the first observation, by Bradley, 
in 1719, the smallest star was near the lower arrow, as 
represented. In 1756 it occupied a very difFerent posi- 
tion, as the drawing shows, and so on to 1844, as repre- 
sented on the map. The periodic time of this system is 
supposed to be 145 years. 

3. Fig. H is another Binary System of a similar 
kind. Jn 1780 the smaller star was seen on the right, 
just above the lower arrow. In 1804 it was near that 
date on the map ; in 1822, it was nearly opposite the 
first position, and so on to 1843. This system is found 
in the Serpent Bearer, and has a period of 93 years. 

4. The learner should here be reminded that these 
are not systems of planets around suns, but of sun around 
sun ; and that their component stars may not only be as 
far apart as our Sun and Sirius, but that they are pro- 
bably each the centre of his own planetary system, like 
that which revolves around our central orb. 

5. The double and multiple stars are of various col- 



158 ELEMENTARY ASTRONOMY. 

ors, beautifully contrasting with each other. The most 
common are orange, blue, green, and red. Some single 
stars are found of a crimson hue, even much redder than 
Aldebaran appears to the naked eye. 



LESSON CXXIV. 

VARIABLE OR PERIODICAL STARS. 

1* Variable stars are those which undergo a regular 
periodical increase and diminution of lustre, involving, 
in one or two cases, a complete extinction and revival. 

2. One of the most remarkable of these is the star 
Omicron in the Whale. It appears about twelve times in 
eleven years, remains at its greatest brightness about a 
fortnight, being then, on some occasions, equal to a large 
star of the second magnitude. It then decreases for 
about three months, when it disappears. In about five 
months it becomes visible again, and continues to in- 
crease during the remaining three months of its period. 

3. Another remarkable periodic star is that called 
Algol, in the constellation Perseus. It is usually visible 
as a star of the second magnitude, and such it continues 
for the space of 2 days 14 hours, when it suddenly begins 
to diminish in splendor, and in about 3^ hours it is re- 
duced to the fourth magnitude. It then begins again to 
increase, and in 3£ hours more is restored to its usual 
brightness, going through all its changes in 2 days 20 
hours and 48 minutes, or thereabouts. There are several 
other variable stars, which we have not room here to 
mention. 

4. The cause of these periodic variations in the 
brightness of some of the stars is not known. Some 
suppose them to be occasioned by opaque bodies revolv- 
ing around them, and cutting off a portion of their light 
from us ; while others are of opinion that those distant 
suns emit less light from one of their sides than from the 
other, and by a revolution upon their axes present us 
alternately with their full and their diminished lustre. 



TEMPORARY STARS. 159 

LESSON CXXV. 

TEMPORARY STARS. 

1. Temporary stars are those which have appeared 
from time to time, in different parts of the heavens, blaz- 
ing forth with extraordinary lustre, and after remaining 
for a while apparently immovable, have died away, and 
left no traces of their existence behind. 

2. A star of this kind, which appeared in the year 
125 B. C, led Hipparchus to draw up a catalogue of the 
stars, the earliest on record. In A. D. 389 a similar 
star appeared near the largest star in the Eagle, which, 
after remaining for three weeks as bright as Venus, dis- 
appeared entirely from view. 

3. On the 11th of November, 1572, Tycho Brahe, a 
celebrated Danish astronomer, was returning in the even- 
ing from his laboratory to his dwelling-house, when he 
was surprised to rind a group of country people gazing 
upon a star which he was sure did not exist half an hour 
before. It was then as bright as Sirius, and continued 
to increase till it surpassed Jupiter in brightness, and 
was visible at noon-day. In December of the same year 
it began to diminish, and in March, 1574, had entirely 
disappeared. 

This remarkable star was in the constellation Cas- 
siopeia, about 5° northeast of the star Caph. The place 
where it once shone is now a dark void ! 

4. " It is an extraordinary fact/ 5 says Dr. Goode, 
" that within the period of the last century, not less than 
thirteen stars, in different constellations, seem to have 
totally perished, and ten neio ones to have been created. 
In many instances it is unquestionable, that the stars 
themselves, the supposed habitations of other kinds or 
orders of intelligent beings, together with the different 
planets by which it is probable they were surrounded, 
have utterly vanished ; and the spots they occupied in 
the heavens have become blanks. What has befallen 
other systems, will assuredly befall- our own. Of the 



160 ELEMENTARY ASTRONOMY. 

time and manner we know nothing, but the fact is incon- 
trovertible ; it is foretold by revelation ; it is inscribed 
in the heavens ; it is felt through the earth." 



LESSON CXXVI. 

FALLING OR SHOOTING STARS. 

The subject of Shooting Stars is here introduced, 
not because it properly belongs here, by the laws of phi- 
losophical classification, but because the student will be 
more apt to look for it in this connection than in any 
other part of the work. We must say but little, how- 
ever, as its full discussion falls not within the compass of 
our design. 

1. Falling or Shooting Stars are not properly stars, 
of any kind, but meteors, within a short distance of the 
earth. A meteor is a fiery or luminous body flying 
through the atmosphere. 

2. Although the number of shooting stars observable 
in a single night is usually small, there have been in- 
stances in which they fell in such numbers as to be 
denominated Meteoric Showers. One of these occurred 
November 13th, 1833. On that morning, says Professor 
Olmsted, from two o'clock until broad daylight, the sky 
being perfectly serene and cloudless, the whole heavens 
were lighted with a magnificent display of celestial fire- 
works. At times the air was filled with streaks of light, 
occasioned by fiery particles darting down so swiftly as 
to leave the impression of their light on the eye (like a 
match ignited and whirled before the face), and drifting 
to the northwest like flakes of snow driven by the wind ; 
while, at short intervals, balls of fire, varying in size 
from minute points to bodies larger than Jupiter and 
Venus, and in a few instances as large as a full moon, 
descended more slowly along the arch of the sky, often 
leaving after them long trains of light, which were, in 
some instances, variegated with different prismatic 
colors.* 

* Introduction to Astronomy, p. 282. 



OF CLUSTERS OF STARS. 161 

3. Of the nature of these meteors very little is known. 
They are supposed to descend from some point beyond 
the limits of our atmosphere, and to be ignited by their 
rapid motion, as they come in contact with it. They ex- 
plode, and are resolved into small clou Is, it is thought, at 
the height of about thirty miles above the earth. 

Professor Olmsted thinks they are caused by some 
rare body like the tail of a comet, or the zodiacal light, 
falling in the way of the Earth in her annual journey 
around the Sun. 



CHAPTER III. 
OF CLUSTERS OF STARS, AND NEBULAE. 

LESSON CXXVII. 

OF CLUSTERS OF STARS. 

(Map 16.) 

1. In surveying the concave of the heavens in a clear 
night, we observe here and there groups of stars, forming 
bright patches, as if drawn together by some cause other 
than casual distribution. Such are the Pleiades and 
Hyades in Taurus, the former of which may be seen at 
I, on the map. These are called Clusters of Stars. 
The constellation Coma Berenices is another such 
group, more ditfused, and consisting of much larger 
stars. The luminous spot called the Bee Hive, in Can- 
cer, is somewhat similar, but less definite, and requires 
a moderate telescope to resolve it into stars. In the 
sword-handle of Perseus, is another such spot or cluster, 
which requires a rather better telescope to resolve it into 
distinct stars. 

2. There are a great number of these objects, which 
have been mistaken for comets, as through telescopes of 



162 ELEMENTARY ASTRONOMY. 

moderate power they appear like the comet of 1585, Map 
15, or like small round, or oval, nebulous specks. Sir 
John Herschel observes that Messier has given a list of 
103 objects of this sort, with which all who search for 
comets ought to be familiar, to avoid being misled by 
their similarity of appearance. That they are not 
comets, however, is evident from their fixedness in the 
heavens, and from the fact that when we come to ex- 
amine them with instruments of great power, they are 
perceived to consist entirely of stars, crowded together so 
as to occupy almost a definite outline, and to run up to 
a blaze of light in the centre, where their condensation 
is usually the greatest. 

3. Many of these clusters are of an exactly round 
figure, and convey the complete idea of a globular space 
filled full of stars, insulated in the heavens, and consti- 
tuting in itself a family or society apart from the rest, 
and subject only to its own internal laws. 

4. It would be a vain effort to attempt to count the 
stars in one of these globular clusters. They are not to 
be reckoned by hundreds ; and on a rough calculation, 
grounded on the apparent intervals between them at the 
borders, and the angular diameter of the whole group, it 
would appear that many clusters of this description must 
contain at least from ten to twenty thousand stars, com- 
pacted and wedged together in a round space, whose an- 
gular diameter does not exceed eight or ten minutes, or 
an area equal to a tenth part of that covered by the 
Moon. 

5. Some of these clusters are of an irregular figure, 
as may be seen at J, on the map. These are generally 
less rich in stars, and especially less condensed towards 
the centre. They are also less definite in point of out- 
line. In some of them the stars are nearly all of a size, 
in others, extremely different. It is no uncommon thing 
to find a very red star, much brighter than the rest, 
occupying a conspicuous situation in them. 

6. It is by no means improbable that the individual 
stars of these clusters are suns like our own, the centres 
of so many distinct systems ; and that their mutual dis- 



OF NEBULA. 163 

tances are equal to those which separate our Sun from 
the nearest fixed stars. Besides, the round figure of 
some of these groups seems to indicate the existence of 
some general bond of union in the nature of an attractive 
force.* 

7. Figure J on the map, is a representation of the 
cluster in Coma Berenices already referred to ; and Fig- 
ure K is a magnificent cluster in Capricornus, contain- 
ing more than a thousand fixed stars. 



LESSON CXXVIII. 

OF NEBULA. 

(Map 16.) 

1. The term Nebula is applied to those clusters of 
stars that are so distant as to appear only like a faint 
cloud or haze of light. In this sense some of the clusters 
heretofore described may be classed as nebulae, and in- 
deed it may be said of all the various kinds of nebulas, 
that it is impossible to say where one species ends and 
another begins. 

2. Resolvable Nebulce are those clusters the light of 
whose individual stars is blended together, when seen 
through a common telescope, but which, when viewed 
through glasses of sufficient power, can be resolved into 
distinct stars. 

3. Irresolvable Nebulce are those nebulous spots which 
were formerly supposed to consist of vast fields of matter 
in a high state of rarefication, and not of distinct stars. 
But it is exceedingly doubtful whether any nebulae exist 
which could not be resolved into stars, had we telescopes 
of sufficient power. The following remarks, taken from 
a lecture recently delivered in Dublin, by Dr. Scoresby, 
in relation to the powers of Lord Rosse's mammoth teles- 
cope, will reflect light upon the subject under considera- 
tion. " About the close of last year, the Earl of Rosse 

* Herschel's Treatise. 



164 ELEMENTARY ASTRONOMY. 

succeeded in getting his great telescope into complete 
operation, and during the first month of his observations 
on fifty of the unresolvable nebulae, he succeeded in 
ascertaining that forty-three of them were already re- 
solvable into masses of stars. Thus is confirmed the 
opinion, that we have only to increase the powers of the 
instrument to resolve all the nebulse into stars, and the 
grand nebular hypothesis of La Place into a splendid as- 
tronomical dream." 

Figure L on the map is a representation of the great 
nebulae in Andromeda, generally considered as irresolv- 
able. It resembles a comet, and may be seen under 
favorable circumstances by the naked eye, like a small 
faint cloud. The stars seen within its limits are sup- 
posed to be beyond it, and consequently seen through it. 

4. Nebulas are again distinguished as Single and 
Double Nebula, The former consist of one cluster 
standing alone, while in the latter case two or more seem 
to be united, or in a state of near proximity, as in Figure 
M. Of the Double Nebulae there is almost every 
possible variety of form and proportionate magnitude. 
The specimen given is a representation of the double 
nebulae in the Greyhound. 

5. Figure N is a representation of what are called 
Hollow Nebulce. This specimen may be found in the 
constellation Sagittarius. 

6. Stellar Nebulae, or Nebulous Stars, are such as 
present the appearance of a thin cloud with a bright 
star in or near the centre. They are round or oval 
shaped, and look like a star with a burr around it, or a 
candle shining through horn. Figures O and P on the 
map are specimens of this class. O is in Cancer, and 
P in Gemini. 

7. The Sun is considered by astronomers as belong- 
ing to this class of nebulous stars, and the Zodiacal 
Light, of which we have spoken in Lesson CVI, has 
been regarded as of the nature of the gaseous matter 
with which the nebulous stars are surrounded. It is 
supposed that if we were as far from the Sun as we are 
from the Stellar Nebulae, he would appear to us only as 
a small and nebulous star ! 



OF NEBTTL-E. ' 165 

8. Planetary Nebula, says Dr. Herschel, are very 
extraordinary objects. They have, as their name im* 
ports, exactly the appearance of planets ; round or 
slightly oval discs, in some instances quite sharply ter- 
minated, in others a little hazy at the borders, and of a 
light exactly equable or only a very little mottled, which, 
in some of them, approaches in vividness to that of the 
actual planets. Whatever be their nature, they must 
be of enormous magnitude. Granting these objects to 
be equally distant from us with the stars, their real 
dimensions must be such as would fill, on the lowest 
computation, the whole orbit of Herschel. 

Figure Q, on the Map, is intended as a specimen of 
Planetary Nebulae, though, it must be confessed, it is 
not easy to get up a very striking resemblance. 

9. Annular Nebula also exist, but are seldom to be 
met with. The most conspicuous of this class is to be 
found exactly half-way between Beta and Gamma, in the 
Lyre, and may be seen with a telescope of moderate 
power. It is small, and particularly well defined, so as 
in fact to have much more the appearance of a flat oval 
solid ring than of a nebula. The space within the ring 
is filled with a faint hazy light, uniformly spread over it, 
like a fine gauze stretched over a hoop.* 

10. Figure R is a representation of a very remark- 
able nebula in the head of the Greyhound, about six 
degrees below Mizar, the middle star in the tail of the 
Great Bear, It consists of a large and bright globular 
nebula surrounded by a double ring, at a considerable 
distance from the globe, or rather a single ring divided 
through about two fifths of its circumference, and having 
one portion, as it were, turned up out of the plane of the 
rest. A faint nebulous atmosphere, and a small round 
nebula near it, like a satellite, completes the figure. 

11. Figure S is another remarkable nebulae in the 
constellation of the Fox. The two round spots about 
the foci of the ellipse or oval, exhibit but a faint and 
dusky light, while the portions about the ends of the 
transverse axis are remarkably bright and uniform. 

* Sir J. Herschel. 



166 ELEMENTARY ASTRONOMY. 

12* Figure T represents a wonderful nebula in the 
Milky Way. Its form is fantastic, and it has several 
openings, through which, as through a window, we seem 
to get a glimpse of other heavens, and brighter regions 
beyond. 

13. The number of nebulous bodies is unknown, per- 
haps we should say innumerable. They are especially 
abundant in the Galaxy or Milky Way. Sir W. Her- 
schel arranged a catalogue showing the places of two 
thousand of these objects* They are of all shapes and 
sizes, and of all degrees of brightness, from the faintest 
milky appearance to the light of a fixed star. 

14. Star Dust is a name given to those exceedingly 
faint nebulous patches that appear to be scattered about 
at random in the far distant heavens. They have no 
definite boundary, and are well represented by the gray 
portions of the map, between the various specimens of 
nebulae. The map was printed light on purpose to 
furnish specimens of Star Dust, or of nebulse so remote 
as to be barely visible through the best telescopes. This 
class of nebulous appearances seems to lie in the back 
ground, far beyond others that are more distinctly visible. 

By placing the learner at a proper distance from the 
map, the idea we wish to convey will be readily under- 
stood. 

15. This map may be used to very good advantage 
to illustrate the uses and powers of the telescope, in re- 
solving nebulas into stars. Place the pupil at the dis- 
tance of from fifteen to twenty feet, according to the 
strength of the light, so that he will see the clusters J and 
K only as faint cloudy patches. Let him then make 
what he may call a telescope of low power, by rolling 
up a sheet of paper, and looking through the tube thus 
formed. Shutting the surrounding light from his eye 
will enable him to see the nebulous spots far more dis- 
tinctly. Then, instead of a telescope of higher power, 
let him approach half way to the map, and look again 
through his paper tube. If the light is good, J and K 
will be mostly resolved into stars. By approaching still 
nearer, more stars will be seen where it appeared nebu- 



OF NEBULA. 167 

lous before, and at length the Star Dust will be seen 
lying beyond the more distinct nebulae, in remote regions 
of space. 

It must not be supposed, however, that barely shut- 
ting the surrounding light from the eye is the principle 
upon which the telescope reveals objects otherwise invisi- 
ble ; the object in these exercises is merely to show that 
as the nearer we are to an object the more distinct the 
vision, so the better the telescope (an instrument which 
seems to bring objects towards us) the more perfect 
the view we have of the different kinds of nebulae, and 
the more likely they are to be resolved into distinct stars. 

16. The nebulae, says Sir John Herschel, furnish in 
every point of view an inexhaustible fielchof speculation 
and conjecture. That by far a larger share of them con- 
sist of stars there can be little doubt ; and in the inter- 
minable range of system upon system, and firmament 
upon firmament, which we thus catch a glimpse of, the 
imagination is bewildered and lost. 

17. The Milky Way is generally regarded by astron- 
omers as only a specimen of nebulse, of which our Sun 
is one of the stars. This zone of small stars (for such 
it actually is) extends quite around the Solar System, 
as the} nebulous circle of Figure R, on the map, extends 
around the large star in the centre. Like that circle, 
also, the Milky Way is divided through some part of its 
circuit, and has various branches and irregularities. 

The vast apparent extent of the Galaxy, as compared 
with other nebulae, is supposed to be justly attributable 
to its comparative nearness. Were we as far from the 
Solar System as we are from the nebulae in the Lyre, 
Figure R, the Milky Way would doubtless appear as an 
Annular Nebula no longer than that. It may therefore 
with propriety be called " the Great Nebula of the 
Solar System. 55 

But what an idea is here conveyed to the mind of the 
almost boundless extent of the Universe ! Sir W. Her- 
schel estimated that 50,000 stars passed the field of his 
telescope in the Milky Way in a single hour ! And yet 
the space thus examined was hardly a point in this great 



168 ELEB1ENTARY ASTRONOMY. 

zone in the " sun-strown firmament." The mutual 
distances of these innumerable orbs, are probably not 
less than the distance from our Sun to the nearest fixed 
stars, while they are each the centre of a distinct system 
of worlds to which they dispense light and heat. 

Were the Universe limited to the Great Solar Nebula 
it would be impossible to conceive of its almost infinite 
dimensions ; but when we reflect that this vast and 
glowing zone of suns is but one of thousands of such 
assemblages, which, from their remoteness, appear only 
as fleecy clouds hovering over the frontiers of space, we 
are absolutely overpowered and lost in the mighty abyss 
of being ! 

And here we leave the reader to his own reflections, 
barely reminding him that as productions of the Great 
Creator " these are but parts of his ways," — the " work- 
manship of his fingers ;" — that he upholds them all " by 
the word of his power," and that over all these worlds he 
presides in majesty as Great King. And yet so perfect is 
his supervision in each, tnat the Jailing sparrow is 
noticed by his omniscient eye, and the very hairs of our 
head are numbered. While, then, we behold his Wis- 
dom, Power, and Goodness so gloriously inscribed in the 
heavens — while they so loudly " declare his glory," and 
reveal him " in the firmament of his power," let us 
learn to be humble and obedient, to love and serve our 
Maker here, that we may be prepared for the more ex- 
tended scenes of another life, and for the society of the 
wise and good in a world to come. 



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